I did.
After tinkering with it for a while, the only other thing I have noticed is that if I click "continue" on the exception dialog box I can look through what it exported before it encountered the exception. It seems to be related to some Pokemon. For instance:
I start from the beginning -- fresh install of KeySAV2, save1, save2, successful decryption, export attempt --> exception. Last line that appears in the output box shows "Box 11 3,6 ..."
I move everything from box 11 to box 12. Start from the beginning again -- fresh install of KeySAV2, save1, save2, successful decryption, export attempt --> exception. Last line that appears in the output box shows "Box 12 3,6".
None of my Pokemon on any of my cartridges are hacked or non-legit in any way. In fact, all Pokemon on this cartridge were either caught or hatched on this cartridge, so I don't think there could be any corruption of the Pokemon data. I'm going to try to release everything in that box and start over again.