Could be the project file is corrupt in which case there's not a lot you can do. One thing you might try is, and I can't remember exactly where it is as I'm at work and not in front of my pc, to clear the temp files. Its under one of the menu options and I think studio calls them something other then temp. It might be that studio is seeing a corrupted copy that is still hanging around. So clear out the cache/temp files whatever it calls them and you might get lucky.