Not sure if it is something you or modders would be able to fix, but probably a good idea for others to be aware of, at least until a solution is found.Expertise skills classes are generated automatically when game is launched, based on loaded bot models and parts. So if modder changed bot model or part id, and you had expertise trained you will get such error. There is not much i can do about it as RenPy loads save games in rather opaque way, but i will investigate some way to silently ignore it, simply removing orphan expertise. No promises on this though.