I am pretty sure it's because it should be RawPotatoes NOT RawPotato. There was apparently some renaming of internal names lately it seems (last 1 or 2 version of game).
Edit:
You can try to see if you can fix it yourself by checking Defs/RecipeDefs/Recipes_AnimalH.xml for any occurence of RawPotato and changing it to RawPotatoes. It should fix it.
Edit:
You can try to see if you can fix it yourself by checking Defs/RecipeDefs/Recipes_AnimalH.xml for any occurence of RawPotato and changing it to RawPotatoes. It should fix it.