1. Copy the corrupted FLA file.
2. Change the extension on the copy to .zip instead of .fla
3. Open the >Library directory and (this is tricky) move the .xml files somewhere else one at a time. Every time you move one, go up one directory and try and open your .xfl file. When it finally opens it means that you found the corrupt (or one of the corrupt) files.
4. Put everything back where it's supposed to be.
5. Open the corrupt file(s) in a text editor and find the empty [Frame] tag.
6. Delete it/them.
7. After this is done for each corrupt file, your .xfl file will open and you can save it as whatever you want.
8. In "Symbol Editor" mode, DO NOT HAVE EMPTY FRAMES ON FRAME 1!!!! That's what causes the problem (I think).
A little more detail on step 7. Most text editors have a "Find" option. In most editors it's Ctrl/Cmd + F. Search for occurances of "Frame". Delete "empty" tags. If you don't understand what that means, basically it'll have something like this:
QUICK REVISION: Blogger thought I was trying to enter actual XML, so the beginning of each line in your file will have the "<" instead of "[". Sorry....
If there is a whole bunch of code in between the "Dom" tags then leave it there (the indentation will give you a hint, and remember these tags could be hundreds of lines apart). An example of what to leave alone will look like this:
INSERT HUNDREDS OF LINES OF CODE (OR TENS OR FIFTIES, WHO KNOWS)
Good luck. Message me if you have any questions.