Thank you for the reply, but I probably should have mentioned that I had already read and tried all these options. None worked.
As it turns out, I needed to change my billing address.
I live outside the US and had listed my foreign address in my return. This is why it didn't accept payment with my American credit card. I had to go back and erase my foreign address and add an American billing address. Luckily I do have one, and the credit card info was finally accepted, but I don't know what to tell the other users who don't have an American address to list.
