wow, this is surreal.
Called my bank. They said something just wasn't being sent correctly and asked if the online vendor was using the "Verified by Visa" system. I wasn't sure, so I signed up for it, then tried again tonight. No go. Called them again. This time, they said that the transaction system was at fault. They were being very vague, probably so as not to give away security information. But they said that it was neither the Vendor's or Bank's fault. It was that the information being sent to the bank was not the correct format or something like that.
They suggested that I should try to contact the vendor to see if they would do a manual transaction. When I suggested that maybe I should try another bank, they said that another credit card may have the same problem, and they stressed that it wasn't the bank's fault.
Any chance I can just mail you a money order?
I swear, this feels just like the Twilight Zone.