From what indivi has said it sounds like your save files are from too many versions back assuming you are trying to update to version 43.1 that is 14 versions skipped from version 29.2, so the save file isn't compatible anymore. But if you're on desktop you can navigate to the folder with the missing file, and put a dummy file in there to trick the game into thinking everything's fine. Then just save your game and it should work.