This error message may occur when attempting to download an eBook using a previously used download link with a different Adobe ID. For example, suppose a customer purchases the eBook 'The Art of War' and downloads it using Adobe ID 'firstname.lastname@example.org' but later attempts to download it on their laptop using the same link with Adobe ID 'email@example.com.' In that case, they will receive this error message. To resolve the issue, the customer must use the same Adobe ID they used previously, in this case, 'firstname.lastname@example.org'.
Alternatively, if a user downloads a book before authorizing Adobe Digital Editions, it will be linked to an "anonymous" account and only exist in the machine library. The title will have been deleted if ADE was reinstalled or opened on a different device.