ADE can see some devices, but not others

I want to transfer a book downloaded ontp my PC to my Galaxy Tab A. My PC can see the Galaxy, but  ADE can't. However, ADE can see my NOOK when I attach that. My Galaxy is Authorized and I have been able to download books OK in the past. I have reinstalled ADE, check sync is enabled and shut down and restarted everything several times. Any one have any ideas, please?