Ahhh, Formal White, my favorite theme due to the fixed block width! I still use it, as I hate the way all the responsive themes expand their blocks widths for no good reason.
If you use any of the extra question types from OU, I think there were four of them, they can cause a little problem, as with the latest version of Moodle they are now built in. The upgrade didn't seem to like or know how to handle them already being there.