Does it happen all the time?
Does it happen with one specific drawing all the time?
When was the last time you rebooted the computer?
If you were losing data in the other files I would make the autosave time very short, like 1 minute, this would save all of you file every minute.
I would suggest that you may want to think about reinstalling AutoCAD if it crashes everytime you try to close it. I have had it crash once and a while, but the only time I've had it happen consistantly was with a corrupt drawing file. My solution was to select all the entities in the drawing file and copy clip them into a blank drawing. This fixed the problem for me.
Kevin Petursson
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"Everyone says quotable things everyday, but their not famous... so nobody cares."... Some Person