I opened my scene and got an error message: "error loading biped". Dug around and found the reason for this and a solution:

For a Clean Save of a corrupted scene file (the opening biped error),

1. Remove biped.dlc from "\3ds Max 9\stdplugs" Don't delete it, just move it out of there so max won't load it, you'll need it again.

2. Load up Max and load your scene with the problem.

3. Select all of your objects in the scene but NOT any bipeds.

4. Go to File: Save Selected and of course save.

5. Exit Max, Move biped.dlc back where it was and load up max and your new scene.

Everything works and you can add new bipeds. So of course, save progressive copies of your work and check the autobacks. But if worse comes to worse and all of your recent files are effected, this will only set you back your animations.
Interesting bug, and apparently, it's been around for a little while and hasn't been fixed. I'm just glad I don't do any character animation other than generic walking people... Imagine losing the animation on some fight choreography or something equally as complex...