it is probably a wrong parameter settings somewhere.
cell parameters :
1/ how many TRX with GPRS enabled in your cell ?
2/ MAX PDCH = ?
3/ MAX PDCH HIGH LOAD = ?
4/ MIN PDCH = ?
5/ GPRS HIGH LOAD and GPRS LOW LOAD (I forgot the names of those 2 parameters)
6/ CS PS MARGIN (here also, the name is approximate)
7/ are you using concentric cell ? (= inner zone + outer zone in the same cell)
cell qos :
1/ what is the RTCH ERLANG for each hour of the day ?
2/ what is the value of MAX SPDCH LIMIT for each hour ? (I’ll try to look up this exact indicator name for you, it is a bit confusing…)