When working with UserControls in VS, you can easily get yourself is a "crash loop." The problem is that while debugging, your UserControl takes down VS. When you re-open the solution, your buggy code runs again and again crashes the process. It's difficult to fix the problem when VS keeps crashing, isn't it?
The fix is simple: go out to the file system and delete the .suo file. Next time the solution is brought up, no solution documents will be displayed by default. You can now fix the problem, but be careful not to use the designer until the underlying problem is fixed. Using the designer before the code is fixed could expose you do another crash loop.