Unable to unauthorize to address "check activation" error message

When I tried to open an ebook borrowed from a library (Overdrive), I received a message that said, "Error. Check activation." 

I tried to unauthorize in ADE and couldn't; I just received the "Unable to Erase Authorization.  Please try after some time" message.

I went to regedit and erased the key, as many others on this forum seem to have been instructed do.  This didn't work.

I've tried uninstalling and reinstalling in various combinations with the above steps, and nothing has worked.

Help!