Ray, do you think is might have something to do with a quotation mark? I have quotation marks like "name of the plant" and em dashes like as, Venus flytrap - variety name. Could this be causing the error?
OK, I just removed quotation marks from the name of a product and the payment still failed. The funny thing is, the payment works fine for credit cards and multiple purchases. I am kind of stumped but I think the answer lies somewhere on he pp_confirm.php page.