first of all, check that your init CS and init MCS are not set too high. try to decrease them to CS-2 and MCS-6, or even CS-1 and MCS-1.
second thing : did you activate the NC2 reselection / redirection ? If yes, then try to disable it, just to see.
If it doesn’t change anything, then it’s perhaps a system failure. try to restart/reset your GPRS in the GPU… (or ask advice to your TAC about this, it’s not my field of expertise !)