I'm getting an annoying occurance.
In certain files, ctrl+z will grey out. I'll have to close the file and open it again for it to work again.
I'll be able to undo in my other open files, just at seemingly randomly some files will no longer let me undo.
Sorry for the lack of debug information.
Post here if this happened to you.
I'm seeing this as well.
I am having the same problem. In Adobe Flash Professional CS5, on Windows 7.
This seems to conincide with not beeing able to select movieclips on stage.