This sounds like an old C* problem when your workspace get’s corrupted in some way. You can try to go back to a previous saved version of your workspace case you have one, if you don’t work in incremental saves check for your .bak files. If neither are options you can always try to find the problem opening your cws with an text editor but it will be really hard to locate the problem unless it’s obvious and you’re familiar on how C* writes stuff to workspace files (cws files are a real mess when it comes to reading).
A good and free thing to try is to reset your copy of C* deleting your .ini files, search this forum on how to do that, I’m sure I have answered this very same question before so as others.
But as far my experience with C* goes (since paint and effect) you’re in pretty nasty situation where you probably will have to redo your roto from scratch all over again, but I hope to be wrong.
Hope it helps.
Cheers,