Runtime Error - first save slot only

I am getting the exact same error. The savefile that started giving me this error was in the first slot, but moving it to another slot also keeps giving the error. I rar-ed and uploaded it here.

Another strange thing about the save: If you go into Continue, click an empty save slot (thus starting a new game), then return to the title page, then go to Continue and click the 'corrupted' save, the save does load, with the correct wizard, equipment, and unlocked levels, but with all quests reset to the starting quests. Quitting the game and running it again after that and trying to continue that save gives you the original error again.

If this is relevant, just before the save got corrupted, I was trying out the alchemy system, and it seemed completely broken. Trying to combine items did nothing, and separating items gave what looked like debug messages in the bottom left but did not actually give/remove items. I figured quitting and reloading the game might fix that, and that's the point where the save wouldn't load anymore.