Thanks for replying.We did not perform any drivetest for this problem. As soon as it presented itself we reserved all the 3G sites for operator use. So only sims with access class 11 configured can access the 3G network at the moment.
We have setup a test cell inside a building on which we are testing the 2G sims.The problem is still there.
You are right, I did not explain the situation correctly. The MS first goes to the 2G network first, but because the 3G network is available inside the building, the MS then tries to LU on the 3G network and gets rejected. The phone then stays in SOS mode.The test cell is not reserved for operator use. So all phones with 2G sims that are on dualmode(2G/3G)are trying to LU on 3G. The only way to avoid it is to set the phone on 2G only.
So I am looking for a solution to this issue.