New transaction is not allowed because there are other threads running in the session.

I am getting this error when trying to start our NOP 4.2 site. I have MultipleActiveResultSets=True in the JSON file for the Connection String. When I reset in IIS, and I navigate to our store URL, I get this error.

Any help would be greatly appreciated.

Error Number:3988,State:1,Class:16
Application startup exception: System.Data.SqlClient.SqlException (0x80131904): New transaction is not allowed because there are other threads running in the session.
   at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
   at System.Data.SqlClient.SqlInternalConnection.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.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)
   at System.Data.SqlClient.TdsParser.TdsExecuteTransactionManagerRequest(Byte[] buffer, TransactionManagerRequestType request, String transactionName, TransactionManagerIsolationLevel isoLevel, Int32 timeout, SqlInternalTransaction transaction, TdsParserStateObject stateObj, Boolean isDelegateControlRequest)
   at System.Data.SqlClient.SqlInternalConnectionTds.ExecuteTransactionYukon(TransactionRequest transactionRequest, String transactionName, IsolationLevel iso, SqlInternalTransaction internalTransaction, Boolean isDelegateControlRequest)
   at System.Data.SqlClient.SqlInternalConnectionTds.ExecuteTransaction(TransactionRequest transactionRequest, String name, IsolationLevel iso, SqlInternalTransaction internalTransaction, Boolean isDelegateControlRequest)
   at System.Data.SqlClient.SqlInternalConnection.BeginSqlTransaction(IsolationLevel iso, String transactionName, Boolean shouldReconnect)
   at System.Data.SqlClient.SqlConnection.BeginTransaction(IsolationLevel iso, String transactionName)
   at System.Data.SqlClient.SqlConnection.BeginDbTransaction(IsolationLevel isolationLevel)
   at Microsoft.EntityFrameworkCore.Storage.RelationalConnection.BeginTransactionWithNoPreconditions(IsolationLevel isolationLevel)
   at Microsoft.EntityFrameworkCore.Storage.RelationalConnection.BeginTransaction(IsolationLevel isolationLevel)
   at Microsoft.EntityFrameworkCore.Storage.RelationalConnection.BeginTransaction()
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.Execute(DbContext _, ValueTuple`2 parameters)
   at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerExecutionStrategy.Execute[TState,TResult](TState state, Func`3 operation, Func`3 verifySucceeded)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.Execute(IEnumerable`1 commandBatches, IRelationalConnection connection)
   at Microsoft.EntityFrameworkCore.Storage.RelationalDatabase.SaveChanges(IReadOnlyList`1 entries)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(IReadOnlyList`1 entriesToSave)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(Boolean acceptAllChangesOnSuccess)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChanges(Boolean acceptAllChangesOnSuccess)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChanges()
   at Nop.Data.EfRepository`1.Insert(TEntity entity) in C:\RankOneSport\Commerce\Source\Repos\Commerce\AllPlayers_42\Libraries\Nop.Data\EfRepository.cs:line 100
   at Nop.Services.Logging.DefaultLogger.InsertLog(LogLevel logLevel, String shortMessage, String fullMessage, Customer customer)
   at Nop.Services.Logging.DefaultLogger.Information(String message, Exception exception, Customer customer)
   at Nop.Web.Framework.Infrastructure.Extensions.ServiceCollectionExtensions.ConfigureApplicationServices(IServiceCollection services, IConfiguration configuration, IHostingEnvironment hostingEnvironment) in C:\RankOneSport\Commerce\Source\Repos\Commerce\AllPlayers_42\Presentation\Nop.Web.Framework\Infrastructure\Extensions\ServiceCollectionExtensions.cs:line 94
   at Nop.Web.Startup.ConfigureServices(IServiceCollection services)
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Hosting.ConventionBasedStartup.ConfigureServices(IServiceCollection services)
   at Microsoft.AspNetCore.Hosting.Internal.WebHost.EnsureApplicationServices()
   at Microsoft.AspNetCore.Hosting.Internal.WebHost.Initialize()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication()

Why do you have MultipleActiveResultSets?  It was removed as per "Release Notes - nopCommerce 3.40 (July 17, 2014)":

 Performance optimization. There's no need to enable MARS (Multiple Active Result Sets). It just adds additional overhead. NOTE for existing store owners. Open \App_Data\Settings.txt file and remove "MultipleActiveResultSets=True" from your connection string.

I removed it. I still receive the error even without it.

Here is a more in-depth error:

Application startup exception: System.InvalidOperationException: A second operation started on this context before a previous operation completed. This is usually caused by different threads using the same instance of DbContext, however instance members are not guaranteed to be thread safe. This could also be caused by a nested query being evaluated on the client, if this is the case rewrite the query avoiding nested invocations.
   at Microsoft.EntityFrameworkCore.Internal.ConcurrencyDetector.EnterCriticalSection()
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(IReadOnlyList`1 entriesToSave)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(Boolean acceptAllChangesOnSuccess)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChanges(Boolean acceptAllChangesOnSuccess)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChanges()
   at Nop.Data.EfRepository`1.Insert(TEntity entity) in C:\RankOneSport\Commerce\Source\Repos\Commerce\AllPlayers_42\Libraries\Nop.Data\EfRepository.cs:line 100
   at Nop.Services.Logging.DefaultLogger.InsertLog(LogLevel logLevel, String shortMessage, String fullMessage, Customer customer) in C:\RankOneSport\Commerce\Source\Repos\Commerce\AllPlayers_42\Libraries\Nop.Services\Logging\DefaultLogger.cs:line 219
   at Nop.Services.Logging.DefaultLogger.Information(String message, Exception exception, Customer customer) in C:\RankOneSport\Commerce\Source\Repos\Commerce\AllPlayers_42\Libraries\Nop.Services\Logging\DefaultLogger.cs:line 237
   at Nop.Web.Framework.Infrastructure.Extensions.ServiceCollectionExtensions.ConfigureApplicationServices(IServiceCollection services, IConfiguration configuration, IHostingEnvironment hostingEnvironment) in C:\RankOneSport\Commerce\Source\Repos\Commerce\AllPlayers_42\Presentation\Nop.Web.Framework\Infrastructure\Extensions\ServiceCollectionExtensions.cs:line 94
   at Nop.Web.Startup.ConfigureServices(IServiceCollection services) in C:\RankOneSport\Commerce\Source\Repos\Commerce\AllPlayers_42\Presentation\Nop.Web\Startup.cs:line 38
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Hosting.ConventionBasedStartup.ConfigureServices(IServiceCollection services)
   at Microsoft.AspNetCore.Hosting.Internal.WebHost.EnsureApplicationServices()
   at Microsoft.AspNetCore.Hosting.Internal.WebHost.Initialize()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication()
crit: Microsoft.AspNetCore.Hosting.Internal.WebHost[6]
      Application startup exception



It looks like it has something to do with DBContext, but I only use it once, and the implementation of it looks correct.

Here is the implementation, inside of ServiceCollectionExtensions.cs:

services.AddDbContextPool<NopObjectContext>(optionsBuilder =>
{
       optionsBuilder.UseSqlServerWithLazyLoading(services);
});

Did you customize?
What is on line 94?
C:\RankOneSport\Commerce\Source\Repos\Commerce\AllPlayers_42\Presentation\Nop.Web.Framework\Infrastructure\Extensions\ServiceCollectionExtensions.cs:line 94

I did not customize. This was lines 94-97:

services.AddDbContextPool<NopObjectContext>(optionsBuilder =>
{
       optionsBuilder.UseSqlServerWithLazyLoading(services);
});