Don't know if this might help - I regularly get this in Amapi. If I'm really lucky I get a warning that says "bad geometry" or "invalid command" or something like that. It just doesn't like what I've done. Then the whole kaboodle ups and disappears. The only way I've found around it is to go back to the original scene and copy each bit into a new doc, see if I can spot the error/s in the models parts and then paste the bits into a completely new doc one by one. It remembers the position, so it's no great hassle. Just a pain.