Unable to Download from a Library to ADE on Windows 10 PC

Unable to download library books (EPUB) to ADE. Started 2 days ago with older version of ADE after working fine for years on same PC. Deleted older version and all files and books I could locate on computer. Installed current version of ADE-4.5.2. Still doesn’t work. When I attempt to download a book, get error message –“error! Check activation”. Have tried deactivating Webroot firewall but not helpful.Nothing changed that I know of when problem started--same PC, same ADE, same library source. I appreciate any ideas.