I was checking the hire/fire actions and when I fired Mrs. Carmon Smith, this error booted up. I don't know why, but when you hire a teacher to the second position without first hiring one into the first position, then fire them, this runs. Even if you still hire the second person. If you hire the first person in the second slot, you can't fire them without this popping up.
I don't know how to use the spoiler tags on this forum, so this is pretty much it.