I also had the problem that it could not shut off DURING a job, but now it does, after following advice found here on $30-$32. Now that all works like a champ. But when the job is done, and it goes to the origin, the laser comes back on and stays on. You can send any command (though admittedly I am not an expert on commands, I have tried M3 S0 - M4 S0 - M5, M03 S0 - M04 S0 - M05), you can close the software (this happens on laserGRBL as well), you can switch to the software that came with the laser and use the button to cycle the laser, but NADA. I have to physically unplug the machine. I have 2 lasers and swapped them out (on the same controller) and it happens to both. Anyone?