scheduled tasks throwing errors

Hi-
All of our enabled scheduled tasks have suddenly started throwing errors, though they show to have successfully executed.

I have restarted the server and it still happens.
Here is an example of the errors in log:
Error while running the 'Delete guests' schedule task. An error occurred while executing the command definition. See the inner exception for details.

System.Data.Entity.Core.EntityCommandExecutionException: An error occurred while executing the command definition. See the inner exception for details. ---> System.Data.SqlClient.SqlException: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. ---> System.ComponentModel.Win32Exception: The wait operation timed out --- End of inner exception stack trace --- at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction) at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose) at System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady) at System.Data.SqlClient.SqlDataReader.TryConsumeMetaData() at System.Data.SqlClient.SqlDataReader.get_MetaData() at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString) at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite, SqlDataReader ds) at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean asyncWrite) at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method) at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method) at System.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior) at System.Data.Entity.Infrastructure.Interception.InternalDispatcher`1.Dispatch[TInterceptionContext,TResult](Func`1 operation, TInterceptionContext interceptionContext, Action`1 executing, Action`1 executed) at System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.Reader(DbCommand command, DbCommandInterceptionContext interceptionContext) at System.Data.Entity.Core.EntityClient.Internal.EntityCommandDefinition.ExecuteStoreCommands(EntityCommand entityCommand, CommandBehavior behavior) --- End of inner exception stack trace --- at System.Data.Entity.Core.EntityClient.Internal.EntityCommandDefinition.ExecuteStoreCommands(EntityCommand entityCommand, CommandBehavior behavior) at System.Data.Entity.Core.Objects.Internal.ObjectQueryExecutionPlan.Execute[TResultType](ObjectContext context, ObjectParameterCollection parameterValues) at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess) at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClassb.<GetResults>b__9() at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation) at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption) at System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__0() at System.Lazy`1.CreateValue() at System.Lazy`1.LazyInitValue() at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext() at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection) at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source) at Nop.Core.PagedList`1..ctor(IQueryable`1 source, Int32 pageIndex, Int32 pageSize) at Nop.Services.Customers.CustomerService.DeleteGuestCustomers(Nullable`1 createdFromUtc, Nullable`1 createdToUtc, Boolean onlyWithoutShoppingCart, Int32 maxNumberOfRecordsToDelete) at Nop.Services.Customers.DeleteGuestsTask.Execute() at Nop.Services.Tasks.Task.Execute(Boolean throwException)

Continued....

It appears to be telling me that it times out while trying to execute, and that there was no "response"...response from what?
I assume these tasks are stored in the database, so is it the database that is't responding?

When I view the scheduled tasks area in admin, it shows that the tasks are successfully completing, but I am not certain that is true.

Can somebody shed some light on this problem for me?

Thanks,
Steve

I've the same, nut didn't have enough time yet to check this problem.

The first need to do it's rim SQL profiler and find which qyery taking so long time and why.

Andrei. I've checked, the reason why nopcommerce struggle to delete guest customers from task because of huge SQL request that I've tried to run separately in Management Studio.
5 minutes and still no result, a was need to stop it manually.
Under some circumstances (unfortunately I didn't check definitely which ones) the next query generated by linq in Nop.Services.Customers.CustomerService.DeleteGuestCustomer just runing for ages.

I believe at the point:
var customers = query.ToList();
line 652.
I think optimization required.

exec sp_executesql N'SELECT 
[Project40].[Id] AS [Id], 
[Project40].[Id1] AS [Id1], 
[Project40].[CustomerGuid] AS [CustomerGuid], 
[Project40].[Username] AS [Username], 
[Project40].[Email] AS [Email], 
[Project40].[Password] AS [Password], 
[Project40].[PasswordFormatId] AS [PasswordFormatId], 
[Project40].[PasswordSalt] AS [PasswordSalt], 
[Project40].[AdminComment] AS [AdminComment], 
[Project40].[IsTaxExempt] AS [IsTaxExempt], 
[Project40].[AffiliateId] AS [AffiliateId], 
[Project40].[VendorId] AS [VendorId], 
[Project40].[Active] AS [Active], 
[Project40].[Deleted] AS [Deleted], 
[Project40].[IsSystemAccount] AS [IsSystemAccount], 
[Project40].[SystemName] AS [SystemName], 
[Project40].[LastIpAddress] AS [LastIpAddress], 
[Project40].[CreatedOnUtc] AS [CreatedOnUtc], 
[Project40].[LastLoginDateUtc] AS [LastLoginDateUtc], 
[Project40].[LastActivityDateUtc] AS [LastActivityDateUtc], 
[Project40].[CustomerStoreId] AS [CustomerStoreId], 
[Project40].[BillingAddress_Id] AS [BillingAddress_Id], 
[Project40].[ShippingAddress_Id] AS [ShippingAddress_Id]
FROM ( SELECT 
  [Project20].[Id] AS [Id], 
  [Limit1].[Id] AS [Id1], 
  [Limit1].[CustomerGuid] AS [CustomerGuid], 
  [Limit1].[Username] AS [Username], 
  [Limit1].[Email] AS [Email], 
  [Limit1].[Password] AS [Password], 
  [Limit1].[PasswordFormatId] AS [PasswordFormatId], 
  [Limit1].[PasswordSalt] AS [PasswordSalt], 
  [Limit1].[AdminComment] AS [AdminComment], 
  [Limit1].[IsTaxExempt] AS [IsTaxExempt], 
  [Limit1].[AffiliateId] AS [AffiliateId], 
  [Limit1].[VendorId] AS [VendorId], 
  [Limit1].[Active] AS [Active], 
  [Limit1].[Deleted] AS [Deleted], 
  [Limit1].[IsSystemAccount] AS [IsSystemAccount], 
  [Limit1].[SystemName] AS [SystemName], 
  [Limit1].[LastIpAddress] AS [LastIpAddress], 
  [Limit1].[CreatedOnUtc] AS [CreatedOnUtc], 
  [Limit1].[LastLoginDateUtc] AS [LastLoginDateUtc], 
  [Limit1].[LastActivityDateUtc] AS [LastActivityDateUtc], 
  [Limit1].[CustomerStoreId] AS [CustomerStoreId], 
  [Limit1].[BillingAddress_Id] AS [BillingAddress_Id], 
  [Limit1].[ShippingAddress_Id] AS [ShippingAddress_Id]
  FROM   (SELECT 
    [Distinct1].[Id] AS [Id]
    FROM ( SELECT DISTINCT 
      [Project17].[Id] AS [Id]
      FROM ( SELECT 
        [Project15].[Id] AS [Id], 
        [Project15].[IsSystemAccount] AS [IsSystemAccount]
        FROM ( SELECT 
          [Project13].[Id] AS [Id], 
          [Project13].[IsSystemAccount] AS [IsSystemAccount]
          FROM ( SELECT 
            [Project11].[Id] AS [Id], 
            [Project11].[IsSystemAccount] AS [IsSystemAccount]
            FROM ( SELECT 
              [Project9].[Id] AS [Id], 
              [Project9].[IsSystemAccount] AS [IsSystemAccount]
              FROM ( SELECT 
                [Project7].[Id] AS [Id], 
                [Project7].[IsSystemAccount] AS [IsSystemAccount]
                FROM ( SELECT 
                  [Project5].[Id] AS [Id], 
                  [Project5].[IsSystemAccount] AS [IsSystemAccount]
                  FROM ( SELECT 
                    [Project3].[Id] AS [Id], 
                    [Project3].[IsSystemAccount] AS [IsSystemAccount]
                    FROM ( SELECT 
                      [Extent1].[Id] AS [Id], 
                      [Extent1].[IsSystemAccount] AS [IsSystemAccount]
                      FROM         [dbo].[Customer] AS [Extent1]
                      LEFT OUTER JOIN [dbo].[Order] AS [Extent2] ON [Extent1].[Id] = [Extent2].[CustomerId]
                      LEFT OUTER JOIN [dbo].[BlogComment] AS [Extent3] ON [Extent1].[Id] = [Extent3].[CustomerId]
                      LEFT OUTER JOIN [dbo].[NewsComment] AS [Extent4] ON [Extent1].[Id] = [Extent4].[CustomerId]
                      LEFT OUTER JOIN [dbo].[ProductReview] AS [Extent5] ON [Extent1].[Id] = [Extent5].[CustomerId]
                      LEFT OUTER JOIN [dbo].[ProductReviewHelpfulness] AS [Extent6] ON [Extent1].[Id] = [Extent6].[CustomerId]
                      LEFT OUTER JOIN [dbo].[PollVotingRecord] AS [Extent7] ON [Extent1].[Id] = [Extent7].[CustomerId]
                      LEFT OUTER JOIN [dbo].[Forums_Post] AS [Extent8] ON [Extent1].[Id] = [Extent8].[CustomerId]
                      LEFT OUTER JOIN [dbo].[Forums_Topic] AS [Extent9] ON [Extent1].[Id] = [Extent9].[CustomerId]
                      WHERE ( NOT EXISTS (SELECT 
                        1 AS [C1]
                        FROM [dbo].[ShoppingCartItem] AS [Extent10]
                        WHERE [Extent1].[Id] = [Extent10].[CustomerId]
                      )) AND (@p__linq__0 >= [Extent1].[CreatedOnUtc]) AND ( EXISTS (SELECT 
                        1 AS [C1]
                        FROM [dbo].[Customer_CustomerRole_Mapping] AS [Extent11]
                        WHERE ([Extent1].[Id] = [Extent11].[Customer_Id]) AND ([Extent11].[CustomerRole_Id] = @p__linq__1)
                      ))
                    )  AS [Project3]
                    WHERE  NOT EXISTS (SELECT 
                      1 AS [C1]
                      FROM [dbo].[Order] AS [Extent12]
                      WHERE [Project3].[Id] = [Extent12].[CustomerId]
                    )
                  )  AS [Project5]
                  WHERE  NOT EXISTS (SELECT 
                    1 AS [C1]
                    FROM [dbo].[BlogComment] AS [Extent13]
                    WHERE [Project5].[Id] = [Extent13].[CustomerId]
                  )
                )  AS [Project7]
                WHERE  NOT EXISTS (SELECT 
                  1 AS [C1]
                  FROM [dbo].[NewsComment] AS [Extent14]
                  WHERE [Project7].[Id] = [Extent14].[CustomerId]
                )
              )  AS [Project9]
              WHERE  NOT EXISTS (SELECT 
                1 AS [C1]
                FROM [dbo].[ProductReview] AS [Extent15]
                WHERE [Project9].[Id] = [Extent15].[CustomerId]
              )
            )  AS [Project11]
            WHERE  NOT EXISTS (SELECT 
              1 AS [C1]
              FROM [dbo].[ProductReviewHelpfulness] AS [Extent16]
              WHERE [Project11].[Id] = [Extent16].[CustomerId]
            )
          )  AS [Project13]
          WHERE  NOT EXISTS (SELECT 
            1 AS [C1]
            FROM [dbo].[PollVotingRecord] AS [Extent17]
            WHERE [Project13].[Id] = [Extent17].[CustomerId]
          )
        )  AS [Project15]
        WHERE  NOT EXISTS (SELECT 
          1 AS [C1]
          FROM [dbo].[Forums_Post] AS [Extent18]
          WHERE [Project15].[Id] = [Extent18].[CustomerId]
        )
      )  AS [Project17]
      WHERE ( NOT EXISTS (SELECT 
        1 AS [C1]
        FROM [dbo].[Forums_Topic] AS [Extent19]
        WHERE [Project17].[Id] = [Extent19].[CustomerId]
      )) AND ([Project17].[IsSystemAccount] <> cast(1 as bit))
    )  AS [Distinct1] ) AS [Project20]
  OUTER APPLY  (SELECT TOP (1) 
    [Project37].[Id] AS [Id], 
    [Project37].[CustomerGuid] AS [CustomerGuid], 
    [Project37].[Username] AS [Username], 
    [Project37].[Email] AS [Email], 
    [Project37].[Password] AS [Password], 
    [Project37].[PasswordFormatId] AS [PasswordFormatId], 
    [Project37].[PasswordSalt] AS [PasswordSalt], 
    [Project37].[AdminComment] AS [AdminComment], 
    [Project37].[IsTaxExempt] AS [IsTaxExempt], 
    [Project37].[AffiliateId] AS [AffiliateId], 
    [Project37].[VendorId] AS [VendorId], 
    [Project37].[Active] AS [Active], 
    [Project37].[Deleted] AS [Deleted], 
    [Project37].[IsSystemAccount] AS [IsSystemAccount], 
    [Project37].[SystemName] AS [SystemName], 
    [Project37].[LastIpAddress] AS [LastIpAddress], 
    [Project37].[CreatedOnUtc] AS [CreatedOnUtc], 
    [Project37].[LastLoginDateUtc] AS [LastLoginDateUtc], 
    [Project37].[LastActivityDateUtc] AS [LastActivityDateUtc], 
    [Project37].[CustomerStoreId] AS [CustomerStoreId], 
    [Project37].[BillingAddress_Id] AS [BillingAddress_Id], 
    [Project37].[ShippingAddress_Id] AS [ShippingAddress_Id]
    FROM ( SELECT 
      [Project35].[Id] AS [Id], 
      [Project35].[CustomerGuid] AS [CustomerGuid], 
      [Project35].[Username] AS [Username], 
      [Project35].[Email] AS [Email], 
      [Project35].[Password] AS [Password], 
      [Project35].[PasswordFormatId] AS [PasswordFormatId], 
      [Project35].[PasswordSalt] AS [PasswordSalt], 
      [Project35].[AdminComment] AS [AdminComment], 
      [Project35].[IsTaxExempt] AS [IsTaxExempt], 
      [Project35].[AffiliateId] AS [AffiliateId], 
      [Project35].[VendorId] AS [VendorId], 
      [Project35].[Active] AS [Active], 
      [Project35].[Deleted] AS [Deleted], 
      [Project35].[IsSystemAccount] AS [IsSystemAccount], 
      [Project35].[SystemName] AS [SystemName], 
      [Project35].[LastIpAddress] AS [LastIpAddress], 
      [Project35].[CreatedOnUtc] AS [CreatedOnUtc], 
      [Project35].[LastLoginDateUtc] AS [LastLoginDateUtc], 
      [Project35].[LastActivityDateUtc] AS [LastActivityDateUtc], 
      [Project35].[CustomerStoreId] AS [CustomerStoreId], 
      [Project35].[BillingAddress_Id] AS [BillingAddress_Id], 
      [Project35].[ShippingAddress_Id] AS [ShippingAddress_Id]
      FROM ( SELECT 
        [Project33].[Id] AS [Id], 
        [Project33].[CustomerGuid] AS [CustomerGuid], 
        [Project33].[Username] AS [Username], 
        [Project33].[Email] AS [Email], 
        [Project33].[Password] AS [Password], 
        [Project33].[PasswordFormatId] AS [PasswordFormatId], 
        [Project33].[PasswordSalt] AS [PasswordSalt], 
        [Project33].[AdminComment] AS [AdminComment], 
        [Project33].[IsTaxExempt] AS [IsTaxExempt], 
        [Project33].[AffiliateId] AS [AffiliateId], 
        [Project33].[VendorId] AS [VendorId], 
        [Project33].[Active] AS [Active], 
        [Project33].[Deleted] AS [Deleted], 
        [Project33].[IsSystemAccount] AS [IsSystemAccount], 
        [Project33].[SystemName] AS [SystemName], 
        [Project33].[LastIpAddress] AS [LastIpAddress], 
        [Project33].[CreatedOnUtc] AS [CreatedOnUtc], 
        [Project33].[LastLoginDateUtc] AS [LastLoginDateUtc], 
        [Project33].[LastActivityDateUtc] AS [LastActivityDateUtc], 
        [Project33].[CustomerStoreId] AS [CustomerStoreId], 
        [Project33].[BillingAddress_Id] AS [BillingAddress_Id], 
        [Project33].[ShippingAddress_Id] AS [ShippingAddress_Id]
        FROM ( SELECT 
          [Project31].[Id] AS [Id], 
          [Project31].[CustomerGuid] AS [CustomerGuid], 
          [Project31].[Username] AS [Username], 
          [Project31].[Email] AS [Email], 
          [Project31].[Password] AS [Password], 
          [Project31].[PasswordFormatId] AS [PasswordFormatId], 
          [Project31].[PasswordSalt] AS [PasswordSalt], 
          [Project31].[AdminComment] AS [AdminComment], 
          [Project31].[IsTaxExempt] AS [IsTaxExempt], 
          [Project31].[AffiliateId] AS [AffiliateId], 
          [Project31].[VendorId] AS [VendorId], 
          [Project31].[Active] AS [Active], 
          [Project31].[Deleted] AS [Deleted], 
          [Project31].[IsSystemAccount] AS [IsSystemAccount], 
          [Project31].[SystemName] AS [SystemName], 
          [Project31].[LastIpAddress] AS [LastIpAddress], 
          [Project31].[CreatedOnUtc] AS [CreatedOnUtc], 
          [Project31].[LastLoginDateUtc] AS [LastLoginDateUtc], 
          [Project31].[LastActivityDateUtc] AS [LastActivityDateUtc], 
          [Project31].[CustomerStoreId] AS [CustomerStoreId], 
          [Project31].[BillingAddress_Id] AS [BillingAddress_Id], 
          [Project31].[ShippingAddress_Id] AS [ShippingAddress_Id]
          FROM ( SELECT 
            [Project29].[Id] AS [Id], 
            [Project29].[CustomerGuid] AS [CustomerGuid], 
            [Project29].[Username] AS [Username], 
            [Project29].[Email] AS [Email], 
            [Project29].[Password] AS [Password], 
            [Project29].[PasswordFormatId] AS [PasswordFormatId], 
            [Project29].[PasswordSalt] AS [PasswordSalt], 
            [Project29].[AdminComment] AS [AdminComment], 
            [Project29].[IsTaxExempt] AS [IsTaxExempt], 
            [Project29].[AffiliateId] AS [AffiliateId], 
            [Project29].[VendorId] AS [VendorId], 
            [Project29].[Active] AS [Active], 
            [Project29].[Deleted] AS [Deleted], 
            [Project29].[IsSystemAccount] AS [IsSystemAccount], 
            [Project29].[SystemName] AS [SystemName], 
            [Project29].[LastIpAddress] AS [LastIpAddress], 
            [Project29].[CreatedOnUtc] AS [CreatedOnUtc], 
            [Project29].[LastLoginDateUtc] AS [LastLoginDateUtc], 
            [Project29].[LastActivityDateUtc] AS [LastActivityDateUtc], 
            [Project29].[CustomerStoreId] AS [CustomerStoreId], 
            [Project29].[BillingAddress_Id] AS [BillingAddress_Id], 
            [Project29].[ShippingAddress_Id] AS [ShippingAddress_Id]
            FROM ( SELECT 
              [Project27].[Id] AS [Id], 
              [Project27].[CustomerGuid] AS [CustomerGuid], 
              [Project27].[Username] AS [Username], 
              [Project27].[Email] AS [Email], 
              [Project27].[Password] AS [Password], 
              [Project27].[PasswordFormatId] AS [PasswordFormatId], 
              [Project27].[PasswordSalt] AS [PasswordSalt], 
              [Project27].[AdminComment] AS [AdminComment], 
              [Project27].[IsTaxExempt] AS [IsTaxExempt], 
              [Project27].[AffiliateId] AS [AffiliateId], 
              [Project27].[VendorId] AS [VendorId], 
              [Project27].[Active] AS [Active], 
              [Project27].[Deleted] AS [Deleted], 
              [Project27].[IsSystemAccount] AS [IsSystemAccount], 
              [Project27].[SystemName] AS [SystemName], 
              [Project27].[LastIpAddress] AS [LastIpAddress], 
              [Project27].[CreatedOnUtc] AS [CreatedOnUtc], 
              [Project27].[LastLoginDateUtc] AS [LastLoginDateUtc], 
              [Project27].[LastActivityDateUtc] AS [LastActivityDateUtc], 
              [Project27].[CustomerStoreId] AS [CustomerStoreId], 
              [Project27].[BillingAddress_Id] AS [BillingAddress_Id], 
              [Project27].[ShippingAddress_Id] AS [ShippingAddress_Id]
              FROM ( SELECT 
                [Project25].[Id] AS [Id], 
                [Project25].[CustomerGuid] AS [CustomerGuid], 
                [Project25].[Username] AS [Username], 
                [Project25].[Email] AS [Email], 
                [Project25].[Password] AS [Password], 
                [Project25].[PasswordFormatId] AS [PasswordFormatId], 
                [Project25].[PasswordSalt] AS [PasswordSalt], 
                [Project25].[AdminComment] AS [AdminComment], 
                [Project25].[IsTaxExempt] AS [IsTaxExempt], 
                [Project25].[AffiliateId] AS [AffiliateId], 
                [Project25].[VendorId] AS [VendorId], 
                [Project25].[Active] AS [Active], 
                [Project25].[Deleted] AS [Deleted], 
                [Project25].[IsSystemAccount] AS [IsSystemAccount], 
                [Project25].[SystemName] AS [SystemName], 
                [Project25].[LastIpAddress] AS [LastIpAddress], 
                [Project25].[CreatedOnUtc] AS [CreatedOnUtc], 
                [Project25].[LastLoginDateUtc] AS [LastLoginDateUtc], 
                [Project25].[LastActivityDateUtc] AS [LastActivityDateUtc], 
                [Project25].[CustomerStoreId] AS [CustomerStoreId], 
                [Project25].[BillingAddress_Id] AS [BillingAddress_Id], 
                [Project25].[ShippingAddress_Id] AS [ShippingAddress_Id]
                FROM ( SELECT 
                  [Project23].[Id] AS [Id], 
                  [Project23].[CustomerGuid] AS [CustomerGuid], 
                  [Project23].[Username] AS [Username], 
                  [Project23].[Email] AS [Email], 
                  [Project23].[Password] AS [Password], 
                  [Project23].[PasswordFormatId] AS [PasswordFormatId], 
                  [Project23].[PasswordSalt] AS [PasswordSalt], 
                  [Project23].[AdminComment] AS [AdminComment], 
                  [Project23].[IsTaxExempt] AS [IsTaxExempt], 
                  [Project23].[AffiliateId] AS [AffiliateId], 
                  [Project23].[VendorId] AS [VendorId], 
                  [Project23].[Active] AS [Active], 
                  [Project23].[Deleted] AS [Deleted], 
                  [Project23].[IsSystemAccount] AS [IsSystemAccount], 
                  [Project23].[SystemName] AS [SystemName], 
                  [Project23].[LastIpAddress] AS [LastIpAddress], 
                  [Project23].[CreatedOnUtc] AS [CreatedOnUtc], 
                  [Project23].[LastLoginDateUtc] AS [LastLoginDateUtc], 
                  [Project23].[LastActivityDateUtc] AS [LastActivityDateUtc], 
                  [Project23].[CustomerStoreId] AS [CustomerStoreId], 
                  [Project23].[BillingAddress_Id] AS [BillingAddress_Id], 
                  [Project23].[ShippingAddress_Id] AS [ShippingAddress_Id]
                  FROM ( SELECT 
                    [Extent20].[Id] AS [Id], 
                    [Extent20].[CustomerGuid] AS [CustomerGuid], 
                    [Extent20].[Username] AS [Username], 
                    [Extent20].[Email] AS [Email], 
                    [Extent20].[Password] AS [Password], 
                    [Extent20].[PasswordFormatId] AS [PasswordFormatId], 
                    [Extent20].[PasswordSalt] AS [PasswordSalt], 
                    [Extent20].[AdminComment] AS [AdminComment], 
                    [Extent20].[IsTaxExempt] AS [IsTaxExempt], 
                    [Extent20].[AffiliateId] AS [AffiliateId], 
                    [Extent20].[VendorId] AS [VendorId], 
                    [Extent20].[Active] AS [Active], 
                    [Extent20].[Deleted] AS [Deleted], 
                    [Extent20].[IsSystemAccount] AS [IsSystemAccount], 
                    [Extent20].[SystemName] AS [SystemName], 
                    [Extent20].[LastIpAddress] AS [LastIpAddress], 
                    [Extent20].[CreatedOnUtc] AS [CreatedOnUtc], 
                    [Extent20].[LastLoginDateUtc] AS [LastLoginDateUtc], 
                    [Extent20].[LastActivityDateUtc] AS [LastActivityDateUtc], 
                    [Extent20].[CustomerStoreId] AS [CustomerStoreId], 
                    [Extent20].[BillingAddress_Id] AS [BillingAddress_Id], 
                    [Extent20].[ShippingAddress_Id] AS [ShippingAddress_Id]
                    FROM         [dbo].[Customer] AS [Extent20]
                    LEFT OUTER JOIN [dbo].[Order] AS [Extent21] ON [Extent20].[Id] = [Extent21].[CustomerId]
                    LEFT OUTER JOIN [dbo].[BlogComment] AS [Extent22] ON [Extent20].[Id] = [Extent22].[CustomerId]
                    LEFT OUTER JOIN [dbo].[NewsComment] AS [Extent23] ON [Extent20].[Id] = [Extent23].[CustomerId]
                    LEFT OUTER JOIN [dbo].[ProductReview] AS [Extent24] ON [Extent20].[Id] = [Extent24].[CustomerId]
                    LEFT OUTER JOIN [dbo].[ProductReviewHelpfulness] AS [Extent25] ON [Extent20].[Id] = [Extent25].[CustomerId]
                    LEFT OUTER JOIN [dbo].[PollVotingRecord] AS [Extent26] ON [Extent20].[Id] = [Extent26].[CustomerId]
                    LEFT OUTER JOIN [dbo].[Forums_Post] AS [Extent27] ON [Extent20].[Id] = [Extent27].[CustomerId]
                    LEFT OUTER JOIN [dbo].[Forums_Topic] AS [Extent28] ON [Extent20].[Id] = [Extent28].[CustomerId]
                    WHERE ( NOT EXISTS (SELECT 
                      1 AS [C1]
                      FROM [dbo].[ShoppingCartItem] AS [Extent29]
                      WHERE [Extent20].[Id] = [Extent29].[CustomerId]
                    )) AND (@p__linq__0 >= [Extent20].[CreatedOnUtc]) AND ( EXISTS (SELECT 
                      1 AS [C1]
                      FROM [dbo].[Customer_CustomerRole_Mapping] AS [Extent30]
                      WHERE ([Extent20].[Id] = [Extent30].[Customer_Id]) AND ([Extent30].[CustomerRole_Id] = @p__linq__1)
                    ))
                  )  AS [Project23]
                  WHERE  NOT EXISTS (SELECT 
                    1 AS [C1]
                    FROM [dbo].[Order] AS [Extent31]
                    WHERE [Project23].[Id] = [Extent31].[CustomerId]
                  )
                )  AS [Project25]
                WHERE  NOT EXISTS (SELECT 
                  1 AS [C1]
                  FROM [dbo].[BlogComment] AS [Extent32]
                  WHERE [Project25].[Id] = [Extent32].[CustomerId]
                )
              )  AS [Project27]
              WHERE  NOT EXISTS (SELECT 
                1 AS [C1]
                FROM [dbo].[NewsComment] AS [Extent33]
                WHERE [Project27].[Id] = [Extent33].[CustomerId]
              )
            )  AS [Project29]
            WHERE  NOT EXISTS (SELECT 
              1 AS [C1]
              FROM [dbo].[ProductReview] AS [Extent34]
              WHERE [Project29].[Id] = [Extent34].[CustomerId]
            )
          )  AS [Project31]
          WHERE  NOT EXISTS (SELECT 
            1 AS [C1]
            FROM [dbo].[ProductReviewHelpfulness] AS [Extent35]
            WHERE [Project31].[Id] = [Extent35].[CustomerId]
          )
        )  AS [Project33]
        WHERE  NOT EXISTS (SELECT 
          1 AS [C1]
          FROM [dbo].[PollVotingRecord] AS [Extent36]
          WHERE [Project33].[Id] = [Extent36].[CustomerId]
        )
      )  AS [Project35]
      WHERE  NOT EXISTS (SELECT 
        1 AS [C1]
        FROM [dbo].[Forums_Post] AS [Extent37]
        WHERE [Project35].[Id] = [Extent37].[CustomerId]
      )
    )  AS [Project37]
    WHERE ( NOT EXISTS (SELECT 
      1 AS [C1]
      FROM [dbo].[Forums_Topic] AS [Extent38]
      WHERE [Project37].[Id] = [Extent38].[CustomerId]
    )) AND ([Project37].[IsSystemAccount] <> cast(1 as bit)) AND ([Project20].[Id] = [Project37].[Id]) ) AS [Limit1]
)  AS [Project40]
ORDER BY [Project40].[Id1] ASC',N'@p__linq__0 datetime2(7),@p__linq__1 int',@p__linq__0='2014-03-17 09:04:40.2311701',@p__linq__1=4

Yes, that SQL is ugly!  It's all those crazy 'join into's

        public virtual int DeleteGuestCustomers(DateTime? createdFromUtc, 
            DateTime? createdToUtc, bool onlyWithoutShoppingCart, int maxNumberOfRecordsToDelete)
        {
...
            var query = _customerRepository.Table;
...
                query = query.Where(c => !c.ShoppingCartItems.Any());
            //no orders
            query = from c in query
                    join o in _orderRepository.Table on c.Id equals o.CustomerId into c_o
                    from o in c_o.DefaultIfEmpty()
                    where !c_o.Any()
                    select c;
            //no blog comments
            query = from c in query
                    join bc in _blogCommentRepository.Table on c.Id equals bc.CustomerId into c_bc
                    from bc in c_bc.DefaultIfEmpty()
                    where !c_bc.Any()
                    select c;

The linq pattern for NOT EXISTS is:  ! .Any     (similar to how it's done on for   !c.ShoppingCartItems.Any()  )

I tested:

var query = _customerRepository.Table;

query = query.Where(c => !c.ShoppingCartItems.Any());
        
query = query.Where(t1 => 
  !_orderRepository.Table.Any(t2 => t2.CustomerId == t1.Id));
  
query = query.Where(t1 => 
  !_blogCommentRepository.Table.Any(t2 => t2.CustomerId == t1.Id));

The result is

SELECT 
    [Extent1].[Id] AS [Id], 
...
    FROM [dbo].[Customer] AS [Extent1]
    WHERE ( NOT EXISTS (SELECT 
        1 AS [C1]
        FROM [dbo].[ShoppingCartItem] AS [Extent2]
        WHERE [Extent1].[Id] = [Extent2].[CustomerId]
    )) AND ( NOT EXISTS (SELECT 
        1 AS [C1]
        FROM [dbo].[Order] AS [Extent3]
        WHERE [Extent3].[CustomerId] = [Extent1].[Id]
    )) AND ( NOT EXISTS (SELECT 
        1 AS [C1]
        FROM [dbo].[BlogComment] AS [Extent4]
        WHERE [Extent4].[CustomerId] = [Extent1].[Id]
    ))

(P.S.  I think you should also add
  query = query.Where(c => !c.Deleted);
No point in deleting if already deleted.  :)


[UPDATE.  P.P.S....
and those !.Any 's can all be appended (if not conditional) - e.g.

query = query
  .Where(t1 => !_orderRepository.Table.Any(t2 => t2.CustomerId == t1.Id))
  .Where(t1 => !_blogCommentRepository.Table.Any(t2 => t2.CustomerId == t1.Id));

Hm .
NewYork, totally agree with you.
But I've tried to do the same, with

query = query.Where(x =>   !_orderRepository.Table.Any(c => c.CustomerId == x.Id));

and I've got OutOfMemory exception, having about 500 gusts to delete. IIS eat 1GB of memory.

Migh be I've missed something when did code refurbishing. Will see it again later or if anyone can provide solution would be lovely.

P.S.

i did it even:

query = query
  .Where( t1 => 
    !_orderRepository.Table.Any(t2 => t2.CustomerId == t1.Id)
    && !_blogCommentRepository.Table.Any(t2 => t2.CustomerId == t1.Id)
  );

Using the " & " will generate the exact same SQL  (I checked it too :)
If you're getting a " OutOfMemory exception", then it's not a database problem.  It's the ASP.NET web app that's throwing that error.  Does the message indicate where the error is occurring?
Are you doing the delete via the scheduled task, or in the System > Maintenance?  (In maintenance, you can try to restrict the date range)

Yes, that's ASP.Net exception. And this is scheduled task.

it's defenitely on fetching data from database.
Exact line is

var customers = query.ToList();

but even 2000 customers should not give so much memory increase.

All I can suppose only that along with Customer EF trying to fetch data from related tables( orderRepository, blogCommentRepository, etc.), which used ".Where" clauses after linq query changing to use .Where instead of joins.

And that is suprising me as i don't use .Include anywhere.