need to know more to answer. are you using the stock room rooted with autonooter? are you using the built-in reader app or the android nook app? when' for various rreasons I've had to reinstall the nb&n app on my blackberry, I've had to enter my credit card number. b&n uses it as the drm key for your purchases. if you erased and deregistered before rooting then tried to opeen the book or if you tried to open it in a version of the app that hadn't opened that file before it would need to make sure you were the purchaser.