QTAgent32.exe has stopped working

Eventually I found the reason

One piece of code was written incorrectly and under some curcumstances caused endless recursion and stack overflow. So if you getting the same error "QTAgent32.exe has stopped working" try to check what is your call stak at this point.

I had a similar problem, so I will present the solution here for anyone else with the same problem.

I would get "QTAgent32.exe has stopped working" whenever trying to run any unit test. This started after I reorganized my solution by pulling out some code into a class library.

This was for a .NET 3.5 solution in VS Premium 2012, update 4.

The fix in the end was to delete the suo file. (This is a hidden file, by the way.)