This error message is received when there is an issue with the authorisation of your Adobe Digital Editions software.
To fix the issue you need to first deauthorise Adobe Digital Editions and then authorise it again.
Please follow the steps on this help page to deauthorise Adobe Digital Editions.
Please follow the steps on this help page to authorise Adobe Digital Editions again.
Once this has been done you need to delete the ebook and redownload it because any ebook file already downloaded prior to reauthorisation may not open. If you need help with the download please follow the steps on this help page to download your ebook to Adobe Digital Editions.
If you are still having difficulty deauthorising or opening your ebook please contact our support team.