activation error for Nook simple touch

I have ADE version 3. I have successfully used it to transfer library books to my Nook Simple Touch in the past, but that was over a year ago. When I tried it recently I got this message: error: Check activation. I thought I had forgotten how to do something, but I cannot figure out what I'm doing wrong. The computer is authorized and has an authorization code, if that makes a difference. Any ideas?