How to fix DRM iBooks now working after 4.2.1 jailbreak
After the recent untethered jailberak of iOS 4.2.1 iBooks with DRM have been giving an issue with jailbroken iPhone's giving the error
"There is a problem with the configuration of your iPhone. Please restore with iTunes and reinstall iBooks"
there is a fairly simple fix available for this which only requires the use of Cydia.
1. Go into Cydia and add " http://repo.insanelyi.com " as a repository in Cydia
2. Download "iBooksFix" which is free and install it
and if for some reason the above method doesn't work for you give this video a try
Source: I Heart Apple