It had to do with the special offer module that enabled the automatic adding of Amanda and Emily's special offer templates to be added directly to the cart when someone ordered the kit. I've turned it off for now until I hear back from the module creator with a fix.
So, the database error message doesn't show anymore, but now people have to do it the old way and add the templates themselves. (Teach me to try to improve the shop, huh
)
Thank y'all so much for the heads up! I didn't even see this!!!