Error saving context in v2.7 Upgrade

I have updated nopcommerce from versión 2.65 to 2.7, but when I run new versión I get an error in this line:

                         this._context.SaveChanges();

from in this code:

public void Insert(T entity)
        {
            try
            {
                if (entity == null)
                    throw new ArgumentNullException("entity");

                this.Entities.Add(entity);

                this._context.SaveChanges();
            }
            catch (DbEntityValidationException dbEx)
            {
                var msg = string.Empty;

                foreach (var validationErrors in dbEx.EntityValidationErrors)
                    foreach (var validationError in validationErrors.ValidationErrors)
                        msg += string.Format("Property: {0} Error: {1}", validationError.PropertyName, validationError.ErrorMessage) + Environment.NewLine;

                var fail = new Exception(msg, dbEx);
                //Debug.WriteLine(fail.Message, fail);
                throw fail;
            }
        }

The type of variable entity is Customer


The error details:

El código de usuario no controló System.Data.Entity.Infrastructure.DbUpdateException
  HResult=-2146233087
  Message=Se produjo un error mientras se actualizaban las entradas. Vea la excepción interna para obtener detalles.
  Source=EntityFramework
  StackTrace:
       en System.Data.Entity.Internal.InternalContext.SaveChanges()
       en System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
       en System.Data.Entity.DbContext.SaveChanges()
       en Nop.Data.EfRepository`1.Insert(T entity) en c:\Users\josep.m.busquets\Documents\Visual Studio 2012\Projects\NopCommerce\Libraries\Nop.Data\EfRepository.cs:línea 41
       en Nop.Services.Customers.CustomerService.InsertGuestCustomer() en c:\Users\josep.m.busquets\Documents\Visual Studio 2012\Projects\NopCommerce\Libraries\Nop.Services\Customers\CustomerService.cs:línea 495
       en Nop.Web.Framework.WebWorkContext.GetCurrentCustomer() en c:\Users\josep.m.busquets\Documents\Visual Studio 2012\Projects\NopCommerce\Presentation\Nop.Web.Framework\WebWorkContext.cs:línea 118
       en Nop.Web.Framework.WebWorkContext.get_CurrentCustomer() en c:\Users\josep.m.busquets\Documents\Visual Studio 2012\Projects\NopCommerce\Presentation\Nop.Web.Framework\WebWorkContext.cs:línea 187
       en Nop.Web.MvcApplication.SetWorkingCulture() en c:\Users\josep.m.busquets\Documents\Visual Studio 2012\Projects\NopCommerce\NopCommerce 2.7\Presentation\Nop.Web\Global.asax.cs:línea 195
       en Nop.Web.MvcApplication.Application_AuthenticateRequest(Object sender, EventArgs e) en c:\Users\josep.m.busquets\Documents\Visual Studio 2012\Projects\NopCommerce\NopCommerce 2.7\Presentation\Nop.Web\Global.asax.cs:línea 141
       en System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
       en System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
  InnerException: System.Data.UpdateException
       HResult=-2146233087
       Message=Se produjo un error mientras se actualizaban las entradas. Vea la excepción interna para obtener detalles.
       Source=System.Data.Entity
       StackTrace:
            en System.Data.Mapping.Update.Internal.UpdateTranslator.Update(IEntityStateManager stateManager, IEntityAdapter adapter)
            en System.Data.EntityClient.EntityAdapter.Update(IEntityStateManager entityCache)
            en System.Data.Objects.ObjectContext.SaveChanges(SaveOptions options)
            en System.Data.Entity.Internal.InternalContext.SaveChanges()
       InnerException: System.Data.SqlClient.SqlException
            HResult=-2146232060
            Message=No se puede insertar el valor NULL en la columna 'Id', tabla 'newGintonic27.dbo.Customer'. La columna no admite valores NULL. Error de INSERT.
Se terminó la instrucción.
            Source=.Net SqlClient Data Provider
            ErrorCode=-2146232060
            Class=16
            LineNumber=1
            Number=515
            Procedure=""
            Server=webserver
            State=2
            StackTrace:
                 en System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
                 en System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
                 en System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
                 en System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)
                 en System.Data.SqlClient.SqlDataReader.TryConsumeMetaData()
                 en System.Data.SqlClient.SqlDataReader.get_MetaData()
                 en System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString)
                 en System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite)
                 en System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean asyncWrite)
                 en System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
                 en System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)
                 en System.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
                 en System.Data.Common.DbCommand.ExecuteReader(CommandBehavior behavior)
                 en System.Data.Mapping.Update.Internal.DynamicUpdateCommand.Execute(UpdateTranslator translator, EntityConnection connection, Dictionary`2 identifierValues, List`1 generatedValues)
                 en System.Data.Mapping.Update.Internal.UpdateTranslator.Update(IEntityStateManager stateManager, IEntityAdapter adapter)
            InnerException:



Any idea?

Thanks