It seems that Barnes and Noble have an interesting take on their version of DRM added to their ebooks. If you buy an ebook from them, you can only download it from them if the credit card you purchased it with is still current. It doesn't matter that you paid for the book previously, and downloaded it once already in this case. No, they have put another barrier in your way.
A reader at The Consumerist named Synimatik is the one with this story:
Yesterday, I tried to download an ebook I paid for, and previously put on my Nook, a few months ago. When I tried, I got an error message stating I could not download the book because the credit card on file had expired. But, I already paid for it. Who cares if the credit card is expired? It has long since been paid for, so the status of the card on file has nothing to do with my ability to download said book. I didn’t see anything in the terms of service about this either, but it’s possible I missed it.
This is just one more reason to either not buy ebooks, or strip the drm off of the ones you purchase so you can you the book you BUY on all your devices without having to purchase multiple copies for no reason and have access to something you already bought when you want it.
You can find the original story at The Consumerist. And they link to a very helpful story at Lifehacker on how to remove DRM from various types of media files.