I'm having same problem.
Any solutions yet?
I was having the same problem and called the nook help desk (1-800-the book). They had me try several things that didn't seem to help. Then they told me how to delete the ADE file from the nook. That didn't seem to help either. . While they were doing some more research, I had ADE up & running on my computer, my nook was plugged into the computer but asleep. I pressed the n to wake up the nook then slid that green arrow thing to the right. A window popped uo on the nook saying i was in USB mode and could now transfer from my computer. When i looked at the computer the 'media' icon was now showing under the bookshelves and a window said something about finding a new device and asking if it should be authorized. I clicked on yes and now can download books successfully.The downloaded books are found on the nook under "library", "my files" , in folder "digital editions".