Adobe never really made a reliable DRM infrastructure around its ADEPT protocol,
and ADE (especially 2.0/2.0.1) is one of the worst programs out there.
The issue was made worse by their recent security breech.
Still, rant over and try some helpful suggestion ....
Do you still have access to your old account, with a revised password?
Is the nook a standard ereader accessed via ADE?
If yes to both those, you may need to deauthorize the nook while plugged into ADE (ctrl-shift-E, cmd-shift-E on Mac),
then reauthorize it. menu/Help/Authorize Device when plugged into ADE: Library/Authorize Device if using the older more reliable ADE 1.7.2
If the nook is a tablet, deauthorize and reauthorize using the mechanism provided in whatever tablet ereader app you use.
If none of this works, backup the content of you nook and try a factory reset.