Hi silverwolff
I also had the annoying problem of it not being recognised.
My solution was the same as j-dickson.
Plug in nook first and make sure it appears as a drive on your desktop
Open the nook folder and see if you have a Digital Editions folder
Delete the Digital Editions folder (or if it contains stuff you want to keep drag it onto your desktop)
Now open Adobe Digital Editions, you should get the 'do you want to authorise' message or a nook icon on the left hand side.
If not have a look at
http://forums.adobe.com/message/2866016 where a guy had similar problems, about half way down it points out that one file may be hidden to mac users as it begins with a '.'.
Have a look