Could possibly be a currupt file. I'm trying to get a crash with your autoback file and I'm not able to reproduce. It would be good if we can find where or what caused the curruption.
Meh, it keeps crashing and corrupting the file. This time when I was about to remove three edge loops and after simplifiying the two areas on the bottom marked with red in my second image. I'm starting to think the file is corrupted even if the autoback doesn't crash instantly.
Usually I'm just trying to simplify the parts I've marked in the image to make the low-poly. I try to make them planar or delete some quads, and then without any previous notice 3ds Max 2017 decides to crash when I make some small action like "undo", deleting an edge loop or changing the selection mode. It's just random.…