Why is Nook Study saying my ADE epub is "not authorized?"

• I have an EPUB file that I purchased from a vendor other than Barnes & Noble.
• I used Adobe Digital Editions to manage the EPUB book onto my Nook Color, which is authorized to open my ADE library.
• I can use ADE to read the EPUB book on my laptop, which also is authorized to open my ADE library.
• However, I cannot use the Nook Study application to read the EPUB book on my laptop.  The error I am getting says, "This textbook is not authorized to be read on this computer."

Any ideas what the problem is here?  I'd be happy to "authorize" the Nook Study installation, if I need to, but I don't know how to authorize an application that is running on an alread-authorized device...