When the debugger in Visual Studio is telling you the problem is in "CSC" instead of pointing you to a particular line of code in a particular file...

...that means it vaguely knows that something in the project is jacked, but it cannot know where for sure as it cannot compile that project because an afferently coupled project can't compile. You shouldn't see this error standalone. It will appear in the debugger with other errors, and you'll just have to fix the other errors first.