This error occurs when you try to open a DRM protected ebook in Apple's iBooks or Apple Books app.

Apple's ebook apps do not support Adobe DRM (the industry standard) so the ebook cannot be read in iBooks/Apple Books.

In order to read your ebook you need to download and install an app that is compatible with Adobe DRM.

If you are using a Mac please install Adobe Digital Editions. Please see our articles on

Installing Adobe Digital Editions (ADE) on your computer

and

Downloading an ebook to Adobe Digital Editions (ADE)

If you are using an iOS device please install our Ebook Reader app. Please see our articles on

Installing Ebook Reader on your device

and

Downloading an ebook to the Ebook Reader app