Apple released iOS 7 yesterday, you may have upgraded your device(s) or will be upgrading in the near future. When an existing OverDrive Media Console (OMC) user upgrades to iOS 7, the app will fail when trying to open a DRM-protected eBook. In the meantime, here are immediate remedies for users:
1) Re-authenticate the app with their existing or a new Adobe ID. Refer to the iOS section of this Help article for assistance. (Recommended)
2) Uninstall and re-install OMC which will also require the user to re-authorize with Adobe. IMPORTANT NOTE: A re-install will clear a user's bookshelf, history, and app settings.
Overdrive apologizes for the inconvenience.