RobotStudio event

ABB S4c

we are having a few problems with our robot Abb S4c
Always same problem can be at home or in working mode we have communication error
teach pendant communication lost. always have to reset 0 axis. have any other user come across this problem. we have had 3 engineers from ABB but are unable to find fault. we have changed all boards inside the robot itself and still have problem. any help would be appreciated.