Cannot download book from my library to my Nook

Help - I recently purchased a Nook book (small version - not tablet) and wanted to download free book from my library.  I went to their website and with the help of the librarian on the phone for 1 hour we downloaded Adobe Digital Edition which is required.  When I picked the book I wanted, it would not download it to my Nook and now I cannot recall what the error message was.  I would like to try doing the whole thing again but which I could have phone support when I do! THANKS, Judy