The version of clr.dll does not match the one mscordacwks.dll was built for

Question

I have a C# console app in Visual Studio 2010 that I can run just fine. When I attempt to run the process in debug mode, I am presented with the following error:

Answer 1

I had VS 2010 SP1 for ages and had rebooted many times. There wasn't any windows update in progress either. I closed all my VS 2010 IDEs and then opened them, and the problem was gone.