Same Issue. Looking at older posts, the answer seems to be - problem with the Nook and not Adobe. I contacted Nook help and was told - Adobe problem. Last year I downloaded an older version of Adobe Digital and it worked great.
Thanks, I'll give it a try.
Here is what worked. I did download 1.7. Then, with Nook plugged into computer, go to Windows explorer. Find the nook. Highlight and delete. Adobe digital editions that is installed on Nook. Open digital editions. I re~added the books I wanted. Unhook Nook properly, and I could open them. I found that answer under someone else's name and can't remember it.
Sent from my U.S. Cellular Android device
Version 1.7.2 is the answer to many problems with ADE 2.0.
ADE2.0 regularly seems to have problems with Sony and Nook devices (and some others too?).
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172