Your purchase could not be completed

We recently purchased an Apple TV. We added our credit card on iTunes for purchases. When we try to rent a movie on iTunes, we get the message: "Your purchase cannot be completed." I signed into iTlunes to view my payment info. For some reason, it won't accept my Visa credit card as a payment method. This is a card we use regularly for our purchases, and we have excellent credit. I removed that Visa credit card and added my Visa debit card. That card worked for one purchase. The next time we tried to rent a movie, we got the same message - purchase could not be completed! When I view my payment info, the 3-digit security code is not there. Can anyone help? Thanks! LF