Have you upgraded with the latests service pack for 3ds max7 ?
There is no way to open a corrupt file but sometimes you can use merge to get the objects from the corrupted file.
If you mange to merge all objects and stil get this error on save the problem might be with one or several of the object nodes in your scene. Make a new box primitive in the scene and attach everything to it. Then delete the box and detach all the objects. This way you have a fresh new object node.
Bare in mind though that neither of these suggestions might work and that your work might be gone
To avoid this:
- use incremental saves (little button with the + in the save dialog)
- increases the number of autobackups and decrease time between backups
Good luck