Problem using Reader on a Nook HD

I've borrowed an ebook from New York Public Library using Cloud Library, and I've followed Cloud Library's instructions for sideloading it from my computer to my Nook HD. The book is now on my Nook HD. When I try to read it, I'm given three app options, including Reader. If I select Reader, I'm asked to enter my Adobe User ID and p/w. But when I do that, I get the message "User not activated". What do I do to "activate" myself? Is it something I have to do on the Nook device or at my Adobe account? Thanks for any help.