I cannot read library books on my Kobo

I suddenly cannot read ebook from my Library on my Kobo. I download the book onto Adobe Digital Editions, transfer it to my Kobo and get the following message:

Your eReader is not authorized to open this book

This book is protected by Adobe Digital Rights Management (DRM). Because you previously deauthorized your eReader, you need to re-import the book using Adobe Digital Editions (ADE). Please visit help.kobo.com for more information.

I have tried de-authorizing and re-authorizing both my computer and Kobo, resetting my Kobo and starting again... Nothing is working!