I bought a used iPad 2, 64gb. It would never authenticate, so I tried to restore it. It only restores about 60%, then gets stuck. I've tried the DFU mode and downloading the latest software version -- 7.0.4. -- With the Wifi Only, Wifi Only-Hardware Revision A, and CDMA versions, iTunes says that "The iPad could not be restored because the firmware file is not compatible." And the GSM version says "iTunes will erase and restore your iPad to iOS 7.0.4 and will verify the restore with Apple." I'm using iTunes 188.8.131.52. I wanted to see if I should restore to the GSM version, and/or if there is anything else I need to do to get the iPad to work. Thanks.