when i try to upload a code to m340 it give me this message 

"This isn't a valid PLC Address, or PLC is busy , or media is off."

whatever i use usb or tcp/ip port, it don't always give me the message but most of the time it does and i have to unplug and replug the cable many time until it upload the code, i am sure it's not a cable problem what can it be?