Deleted it using Titanium Pro. Trying to restore now. Running but taking a long time. Cardock may be a system file also.
Note that using the 3G icon fix from rootzwiki will also result in installation failure.
Sony LT25i “Tsubasa”, stock, rooted, locked bootloader [Android 4.1.2 “Jelly Bean”].
Maximum speed witnessed over LTE: 98.2 Mbps down / 48.5 Mbps up; Average speed over LTE: 72.9 Mbps down / 45.7 Mbps up.
Had you installed the 3G pixel correction that GY mentioned? Also, I don't know how significant it is that you cannot unroot, but that could indicate missing or extra files that stop the update. But, impossible to say!