mount: wrong fs type, bad option, bad superblock on /dev/sdb1, missing codepage or helper program, or other error. In some cases useful info is found in syslog - try dmesg | tail or soConsidering that I've used this camera with the computer plenty of times before, I assumed that this error message meant that the flash card was corrupted. I did an fdisk, but it didn't find anything wrong. Doing a "dmesg | tail", as the message suggested, gave me:
FAT-fs (sdb1): codepage cp437 not found
Codepages are part of the kernel, so this was actually the hint I needed. The problem was that the kernel had been updated, but the system hadn't been rebooted. After a quick reboot, the problem went away.
The lesson is that even in Linux, sometimes a good, clean restart is all that's needed to fix a problem.