in my library I found this advice:
Did you delete the digital editions folder and .adobe folder from the Nook or the computer? You need to delete them both from the Nook. Your ADE ID and your BN ID are different. The BN ID is used to log into the BN site, the ADE id is an Adobe ID. They do not need to be the same. If you've been using your sisters email, you need to continue using it, you can't transfer the books to another user ID.
After you delete the two folders from the Nook, you need to properly eject the Nook from the computer and close ADE. Open ADE and connect the Nook, you should get a window asking you to authorize the device.
Did you follow these instructions?
Go to “My Computer” (or the equivalent on your PC or Mac) and click on the Nook drive.
Find and delete the “.adobe-digital-editions file. (I copied my digital editions folder to my PC and then deleted it from the Nook, in addition to delete the .adobe ID.)
Your Nook should now be visible to ADE, if not
Go back to the Nook drive
Find the “Digital Editions” file and delete it
Nook will be visible
Click “Authorize Device”
Pleas give it a try.
Thank you. I'll try this.