ereader not authorized

My Kobo and computer both share the same ID for the adobe digital editions.  On my computer they both show as authorized devices.  Yet, when I download a library book to the reader, I will get the message: Your eReader is not authorized to open this book.  I have tried unauthorizing and authorizing again both devices.  I have been able to download sometimes in the past.  What can I do to prevent this from happening?