Archie, I am using 3.99Y Beta 10 for my latest project. I have found the ModbusTCPCom1_ComError event does not fire based on device ID. I only get this to fire if I have the wrong IP address but will not fire if the device ID is wrong. Also the ModbusTCPCom1_ConnectionEstablished seems to act only based on IP address as well. It will fire anytime the IP address is correct regardless of the device ID. Hope this makes sense, thank you