No Network coverage in GSM Network mode

My Sony T2 has WCDMA on sim 1 and put GSM on sim 2. Sim 2 loses network coverage completly. this is the same when I do it vice versa e.g. sim 1 -GSM and sim 2 - WCDMA/GSm preffered, then sim 1 loses coverage, seeing as the phone is designed to work as one sim on WCDMA and the other on GSM, whichever slot thats has GSM has no Network completely. I have tried hard reset, PC Companion repiar and reinstall but I'm still only able to have one line with signal having WCDMA. What Can i do