System.Data.Linq not imported

I just installed VS 2012.
In the file <dbname>designer.vb (generated in VS 2010) Visual Studio 2012 displays 100 errors  such as 'System.Data.Linq.DataContext' is not defined, although System.Data.Linq is present in References.

Additional information:

Assembly Load Trace: The following information can be helpful to determine why the assembly 'System.Data.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' could not be loaded.


=== Pre-bind state information ===
LOG: User = IIS APPPOOL\DefaultAppPool
LOG: DisplayName = System.Data.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
 (Fully-specified)
LOG: Appbase = file:///E:/inetpub/IRISEL8/
LOG: Initial PrivatePath = E:\inetpub\IRISEL8\bin
Calling assembly : (Unknown).
===
LOG: This bind starts in default load context.
LOG: Using application configuration file: E:\inetpub\IRISEL8\web.config
LOG: Using host configuration file: C:\Windows\Microsoft.NET\Framework64\v2.0.50727\Aspnet.config
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework64\v2.0.50727\config\machine.config.
LOG: Post-policy reference: System.Data.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework64/v2.0.50727/Temporary ASP.NET Files/root/ea16591a/4859c991/System.Data.Linq.DLL.
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework64/v2.0.50727/Temporary ASP.NET Files/root/ea16591a/4859c991/System.Data.Linq/System.Data.Linq.DLL.
LOG: Attempting download of new URL file:///E:/inetpub/IRISEL8/bin/System.Data.Linq.DLL.
LOG: Attempting download of new URL file:///E:/inetpub/IRISEL8/bin/System.Data.Linq/System.Data.Linq.DLL.
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework64/v2.0.50727/Temporary ASP.NET Files/root/ea16591a/4859c991/System.Data.Linq.EXE.
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework64/v2.0.50727/Temporary ASP.NET Files/root/ea16591a/4859c991/System.Data.Linq/System.Data.Linq.EXE.
LOG: Attempting download of new URL file:///E:/inetpub/IRISEL8/bin/System.Data.Linq.EXE.
LOG: Attempting download of new URL file:///E:/inetpub/IRISEL8/bin/System.Data.Linq/System.Data.Linq.EXE.