I'm having the same problem. It's too bad that no one is giving us an answer! Did you ever find a solution?
I experience the identical fail with my Nook Color and ADE V.4.x
No problem loading library books into ADE on my Win7 laptop. I can read them there no problem.
But when I connect my Nook, ADE does not recognize it as a device, even though my laptop does.
Workaround so far has been to locate the files in Windows Explorer, then open a separate window for the Nook and navigate to:
Computer>MyNOOK>Internal Storage>My Files>Books
(I could find no "digital editions" folder on my Nook)
Then drag and drop the desired ePUB files.
IMO Adobe has delivered a rather poor user experience in this instance and should fix it.
Why, for example, aren't my books shared with my devices in the cloud? Kindle does this with zero effort.
i did exactly what you said. It shows on my Nook but nothing happens when I try to open it.