I'm reposting this after it was taken down last week without explanation and none of the mods will reply to my PMs.
So Illustrator 5 corrupted a file on me last week somehow. I started a project in it and was working fine last week. Now I open the file and when I try to enter into one of my figures with a sequence, Illustrate exits. I really didn't want to lose all the work I put into that figure sequence so I took some time to see if I could revert the file to 4.2. I had some success so I wanted to share how I did it here if it will help anyone else out.
Note: Use at your own risk and back up your files before trying this. While it worked for my simple files containing only animation sequences I'm sure it will fail in some instances especially if you are using new features not present in 4.2.
Let's say I have a file names bike.c3di
Rename the file to bike.c3di.zip and extract to a folder. This is in addition to other backups you make have, you will lose this file in the process.
In this extracted folder modify the en.xlf file, replacing the <tool> section with the 4.2 version shown below
Open your zip file (bike.c3di.zip) in winRAR and replace the en.xlf and manifest.3di files with you modified version. Note: I tried just zipping the folder back up with the windows "Save as Compressed Folder" action and Illustrate says the resulting file is corrupt when you try to open it. I have sen this same behavior with modifying .pzv files. Not sure the root cause but I know this winRAR method works.
Rename bike.c3di.zip back to bike.c3di and it should now open in illustrate 4.2
This makes me wonder if maybe the problem wasn't your original post, but my comment, which made liberal use of the "h" word to describe opening up the c3di zipped contents, modifying them, and then rezipping into a new c3di file.