too many activations error

I still cannot open a book on my Nook Color.  I have always been able to download it through Overdrive, borrowing a book from my library.  Then I download it onto my Nook using Adobe Digital Editions (ADE).  When I do so now, it indicates the book loading, but I only see a blank white page.  Finally, I get a message about too many authorizations or activations.  I was told to go to ADE and click on File, then authorize the Nook.  It has been authorized for several years.  The only options I'm given is to DE-authorize it and re-register.  I hate to do this as I have lots of externally loaded books not purchased from B&N.  Help, please!