ADE doesn't support MTP protocol, that's the reason its not getting mounted in ADE.
You can manually move to book from "C:\Users\<USERNAME>\Documents\My Digital Editions" to your device.
Note: Make sure your device is activated with the same account.
Thanks for your suggestion. When I tried that, the book transferred to my eReader, but when I tried to open it, I got an error message "Protected by Digital Rights Management", and it won't open the book. Is that because my device is not activated with the same account, and how do I do that? Thanks again for your help.
Thanks for starting this thread. Exactly what I needed. Just used the manual directions to download to my Nook Color. When I opened the file on my reader I was prompted for my Adobe ID and password. It worked! Hope your issue is as easily resolved.
Yes, you have to activate the reader with the same Adobe ID.