There are lots of bugs in ADE2.0. These include failing to recognize or misbehaving with various devices.
Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
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
If you really want to use ADE2.0, you can use ADE to process initial .acsm files to .epub files,
and then copy the .epub files to the Nook using a file manager such as Windows Explorer or Finder.
If the books are not DRM, just use the free and superior Calibre instead of ADE.