It looks like you bought it through the webbrowser, not from the device itself. Is that right? Can you check and see if it is a PagePerfect book? Those books cause problems on the HD devices (havent heard of them causing problems on the NT though.) If it is a PagePerfect book, send Alex a PM and see if he can get it fixed for you (or get you a refund.)
Try to deregister and register your nook again. I had the same problem and called customer service. They told me to do this and it worked. Hopefully it solves your problem too.