Apple released iOS on September 18th and many of your Apple users may have upgraded their device(s).
When an existing OverDrive Media Console (OMC) user upgrades to iOS 7, the app will fail when trying to open a DRM-protected eBook. New or first time users of OMC are unaffected by this issue.
We are resolving the issue but 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.
Audiobook users won't notice that anything is different unless they attempt to download parts of audiobooks they already downloaded to OMC before upgrading to iOS 7. A user will receive an error message informing them to download the title again.