a3pl

Hi Some years ago i wrote an aplication on SCADA system to watch some objects. SCADA is communicating with Unitronics PLC's via UniOPC server and GPRS (some in "listen" and some in "call" mode). Recently somePLCs were added to that system and i wrote additional software tomanage that new objects. But now sometimes Im' getting errors: "Communication driver or PLC fault - (103). (Reset the PLC)" Can I find somewhere which PLC is causing that error ? Any suggestions what should I or the engenier who made PLC+modem system check ?