Hi sjpt - it's a Kobo ereader. I don't know where the problem originates but I download the library book at ADE and then drag and drop the book from ADE to my Kobo (as I have always done). The book appears on my Kobo but when I click on it to read I keep getting the same message "The content you are trying to view is locked. Please use your Adobe ID to authorize your ereader with the Kobo desktop application or Adobe digtial editions." I have unauthorized (using control, shift, D) and re-authorized ADE but am still getting the same message. The book works on ADE and I can still read all my other books on my Kobo.
Thanks for any help you can give! It's driving me insane!