Nokia :: Connection Error In N97 Mini

I do not find any working network in a particular place,sometimes the place varies. But, this is not a problem with the network operator because i plugged in my sim card in a different phone and it works fine.At the same time, the n 97 mini constantly gives the error message 'connection error'. However, this problem only occurs in some (one or two) particular places and works fine in other places.But, this is annoying me because the no. of times im getting this error message is increasing day by day. I disconnected bluetooth,wlan,internet connection and factory reset the phone but the problems persist.