Given that DeDRM'ing the books does work, it doesn't look like that's a bug with the DeACSM plugin, more like a bug with the reader.
Are you sure that both DeACSM and the Nook are authorized to the same Adobe account? They probably are, given that you're saying that non-library books work, but you never know ...
Try connecting the Nook to your computer, open the ".adobe-digital-editions/activation.xml" file on the device (hidden folder, so make sure your file browser shows hidden files/folders) and check what ID it displays in the "<adept:user>" entry. Should begin with "urn:uuid:" and then a bunch of letters and numbers.
Then open Calibre, go to Preferences -> Miscellaneous, then click "Open calibre configuration folder", then go to "plugins/DeACSM/account", open the activation.xml that's in there, and check if the "<adept:user>" entry is identical to the one on the Nook.
If that's not the case, you'll probably need to re-authorize the Nook somehow.
If it is (= the entries are identical) then the problem will be something else with the reader and not due to different Adobe IDs.