Ebooks from library will not open "not currently authorized with your Adobe ID"

After years using this Kobo and downloading ebooks from the library, and after no changes to equipment, my eReader says 'This document is protected by Adobe Digital Rights Management and is not currently authorized for use with your Adobe ID.  Please sign-in with the authorized Adobe ID and try again."  So I erased authorization and re-authorized.  No difference.  Then I pressed the Windows button and R, got into Registry Editor, under key HKEY_CURRENT_USER\Software\Adobe\   I deleted the folder called Adept.  Re-authorized Adobe Digital Editions.  Downloaded a new ebook -- same error.