Unfortunately (fortunately?), I cannot reproduce the problem. I really wasn't doing much before. I added a bit of code, 5 sprites to my project, gave them 4 variables and kept trying to enter text into a number variable by accident, but that's really it.
I'm wondering if something didn't save right when my computer hibernated. I have autosaves set to go into my dropbox, but for some reason I have a bunch of .capx.backup[numbers] in the folder with my manually saved .capx between the time of my last good manual save and the corrupted manual save.
All the goodies are here: dropbox.com/sh/dfvgjqnkoqbzbce/LKUQPLr3Zk
It's no burden to me since it was only about 2 hours of simple work (which I've already reproduced), I just thought you should know.