I don't know if anyone else has noticed, but when I go to Upgrade Database again after the error, it says that the database appears up to date. Perhaps the database is up to date and just has not updated in the Admin section?

I thought about just using Easy Populate and reinstalling ZenCart, but all my customer accounts and changes I've made to the site would be gone. So hopefully someone comes up with a fix for this, or I'll have to give in and reinstall after the weekend.