This is just asking the basics but can you elaborate on a few things like what OS, what version of Flash, what's on the layers you're extending, etc. The more detail the better the response. For example I've stretched some video frames before and had some various crashing issues. Flash just didn't like the video. I re-encoded a new video, replaced the old video and it was fine. Odd things like that happen time to time.
I'm running Windows 7..version CS6 Pro
The layers have Text on them that I've converted to Graphics so they can fade in and out when they move on and off the frame
There is a bar/logo at the bottom of the page that must be on all frames so I've been selecting the layers that have the text and the layers that have the bar/logo so everything stays up for the same amount of time
The whole purpose for this is so the text can stay up long enough to read it...I created the original file with no problem but when I re-open it to make those "time-based-adjustments" and they go to Save the file this error occurs and it takes my file with it
Hope this sheds more light on the problem
CS6 Pro was pretty rock solid. I actually just noticed a Flash Pro CS6 update today (not sure when it came out), mostly for device packaging but still you should check if you can apply that patch.
Have you tried saving this file using XFL? Just hit Save-As and hit the drop-down at the bottom and try the XFL format. I prefer this format for a variety of reasons, one of which is it's very easy to store in version management and it externalizes the library assets rather than keeping them all in one "this could blow up and take it all out" single file.
Do you have a CC subscription?