I couldn't find an error log for any of the crashes. I might have deleted it when using CCleaner? If it happened again, however, I will be sure to immediately save the crash log.
In the meantime, for apparently no reason, I have been able to import photos all of a sudden again. It might or might not be related, but I imported a previous catalogue. After importing the catalogue, I tried importing new files, and it worked again.
Problem solved, mystery not solved.