AFT232, Did you get anywhere with this problem? I am having similar problems with my setup and I feel it's with wiring the Proma THC-SD. When the GCode file gets to the torch firing it turns on the torch for .5 second (with no arc, air only) and then my CNC Arduino UNO/breakout board disconnect from the PC. I've narrowed it down to the Proma THC-SD and the Relay switches.