My Kobo gave me a message that the DRM was unauthorized. How do I fix it?
Are you using Digital Editions to transfer books to your Kobo eReader? I so you must authorize your eReader with Adobe.
When you authorize your Kobo eReader, Adobe adds it to the list of devices associated with your Adobe account.
Adobe limits the number of eReaders and computers you can use with their software, which is why this is necessary.
To authorize your eReader:
North America
Europe, Middle East and Africa
Asia Pacific