I get the error message "There is a problem with the configuration of your iPhone. Please restore with iTunes and reinstall iBooks."
My issue on ipad/iphone4 4.2.1 jailbroken with greenpoison now i cant read any purchased books all other files are fine in ibooks ie my pdf's and other non DRM books but the ones i paid for are not working just the restore with itunes and re-install ibooks error ive deleted and re installed ibooks from app store and deleted and reloaded books from ibooks still not working
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This is a known issue and the Chronic Dev Team is looking into it. Greenpois0n does indeed prevent DRM protected books from being read in iBooks
see link below