Yay! A problem with Windows shares, again!
I'm loving it!
[SOLUTION]CIFS VFS: cifs_mount failed w/return code = -22
Seems I've already encountered and fixed this one, but with a different error message.
UPDATE: I just had the same error (with the same share) on a different machine, where I had already configured the "/etc/request-key.conf" file as mentioned in the thread.
There, I just had to execute the mount command again (without any changes) after the above error. Hmpf. I don't like random behavior.