I have this problem too. I saw some things online. They didn't work for me though. Have you tried erase authorization on your nook and computer and then reauthorizing them? It also said to delete the digital editions file from your nook and then disconnect it before you try copying again. It didn't work for me, but maybe you'll have better luck.
i already did all that and it did not work.
Sorry. I was able to get mine to work by downlaoding adobe digital editions version 3.0. Maybe you could try that way?