Ok - now I am realy getting confused.

I create a blank project, added a blank .vb file and inserted your one liner and the try catch (seperatly). I did not add any imports (specificly for the linq) or any references.

The output looks ok

8
The thread 'vshost.RunParkingWindow' (0xff0) has exited with code 0 (0x0).
The thread '<No Name>' (0x1290) has exited with code 0 (0x0).
The program '[3156] Project1.vshost.exe: Managed (v4.0.30319)' has exited with code 0 (0x0).

This is on the development machine (Win2003, 64-bit).

On that same machine i ran my full app (no more linq code as far as I can tell - converted it all, and no more references to linq), but I am getting the error with System.Windows.Forms.dll when running this on the DevMachine in AnyCPU mode.





>To be clear - did this occur when running the skeletal project I suggested. If not then try that. Is so try this:

Module Module1
>    Sub Main()
>        Console.WriteLine(IntPtr.Size.ToString())
>        Try
>            Dim em As System.Linq.ParallelExecutionMode = System.Linq.ParallelExecutionMode.Default
>        Catch ex As Exception
>            System.Diagnostics.Debugger.Break()
>        End Try
>        Console.ReadLine()
>    End Sub
>End Module

Console write should be '4' if running in a 32-bit environment, '8' for 64-bit. The catch may give you a bit more information on the exact nature of the problem if in the IDE (check for inner exceptions)
>
>FWIW I think the path you mention is normal for the framework DLL's - but if the exception occurs in the line that uses System.Linq I don't know there System.Windows.Forms.dll comes into it ?
>Also, FWIW, I ran the above code on a 64-bit WIN7 machine in both 32 and 64 bit modes with no problem.
>Where did you find any references to problems with System.Windows.Forms.dll on 64-bit ?
>
>
>>Before I do that it occured to me that i am developing this on a win2003 64-bit machine. So instead of just building and then installing on another pc i run it right out of VS2010.
>>
>>There i get the following error running as AnyCPU:

>>A first chance exception of type 'System.BadImageFormatException' occurred in System.Windows.Forms.dll
>>'DMS DataEntry.exe': Loaded 'C:\Windows\System32\version.dll', Cannot find or open the PDB file
>>An unhandled exception of type 'System.InvalidOperationException' occurred in DMS DataEntry.exe

>>some research suggests that there is an issue with 64-bit version of System.Windows.Forms.dll. I looked where the file is comming from (in the properties) and it comes from "C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0\System.Windows.Forms.dll" - notice the "x86" - but so do most of the other dlls listed in the references.
>>
>>I also tried to add an exeption routine to my app - ran into problems. But I think i start a seperate thread for that.
>>
>>Thanks.
>>
>>
>>
>>
>>
>>>As per the namespace the ParallelExecutionMode enum *needs* System.Linq. The question was whether use of just that line also causes an exception on the XP/64 machine. See if this one-line project will run:

Module Module1
>>>    Sub Main()
>>>        Dim em As System.Linq.ParallelExecutionMode = System.Linq.ParallelExecutionMode.Default
>>>    End Sub
>>>End Module

Also, as mentioned earlier, look at catching unhandled exceptions in code - that will give you more information on the exception details.
>>>