Yeah, I can easily believe flash would do that. Here's something that I'll often try in that sorta situation- copy and paste the whole damn timeline into a new flash document. It's saved me on a number of occasions. The only thing to remember though is it'll make every frame end at the same point, so if you have a layer that you stopped using halfway through the movie, the last keyframe on that layer will stay right until the end. So before you copy and paste you might wanna stick a blank keyframe at the end of any layers that aren't used right to the end of the movie.
Also, be aware your computer may well not be able to handle such a large copypasta. I had to do this to fix a glitch in 'The Pigpen', which was about the same size, and I had to copy-and-paste the movie in 3 parts.
Anyway, hope this works for you as well as it's worked for me!
GenericJosh
I'd help, but all I could tell you to do is restart the program. Don't export the file till you finish and just "save it". If you export it, all your work will probably be for nothing, but maybe restart the flash, then your computer, and keep trying. I hope for your sake you don't have to start from scratch
tacobuttfish
Thanks, you know I have restarted flash and even tried it in cs3 and cs4, but I've been working almost nonstop for weeks, and haven't restarted my computer, I'll try that, would be wonderful if something so simple solved the problem.