Need help sim/data

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http://forum.xda-developers.com – Hello guys. I was looking around about my problem but it seems that there isn't a solution about my problem. I own a t999 and I have unlocked via a cable. Since the last upgrade to 4.1.1 it seems that whenever there is no call signal and at the same time the data is on and goes below ''E'', the mobile loose the connection with the sim. A msg pop up saying invalid sim please reboot and insert a valid sim. Something like that. I even changed the simple slot but that had nothing to do with. Did anyone found a solution? Is it maybe a bad installation of 4.1.1? Is the way I unlocked (HowTos)