Try deleting the credit card from your B&N account, then add it again.
You could try to use the erase and deregister option, and register your Nook anew. That often solves all kind of weird problems.
This will delete all the data on your Nook! You will have to download your B&N content again! And of course make sure you have a backup of any sideloaded content!
As a temporary workaround you could try to buy a gift card. You can add the gift card to your B&N account. Then the books will be paid with the gift card, and the credit card will only be verified for the DRM.
Last edited by geertm; 02-27-2013 at 02:35 PM.