It started crashing on me again, so I deleted all the diffmap.ini* files from the backup directory. And it then happened again a bit later. Took a while to find a pattern, but at least for me, after cleaning up the diffmap.ini* files and starting VS and opening my project, I can do 3 diffs. The 4th one then crashes. If I instead start over (cleanup diffmap.ini* files), start VS with no files, and open the diff dialog and just cancel (Esc), I can do that 9 times OK, but when I try to cancel the 10th time, VS crashes again.