I just got the problem so I could checked what was wrong and it's due to the fact Teameditor can't find any of the past carshape names (in my case, I replace my whole cars.wad with a complete new one where no carshape have the same name as my previous cars).
In that case only, I missed to specify to reset opened file and thus it can't be closed correctly (weird behaviour anyway).
It will work if you reinstall your past mod but if you install all the new cars at once (like with a whole new cars.wad), it will crash again.
I hope to release a fixed version soon.