Well I didn't go to school much.. ..

Some people have trouble with the smooth stepper locking up on or dropping the signal causing Mach to lock up. Often this is caused by poor grounding but there is a slight flaw in the SS design in that it's sensitive to electrical noise. So if poor grounding in control box or very noisey elctrical components near by they interfere and can in some case's lock the SS.

Personally I only had a one slight issue with this and that was caused by a very noisy compressor switch. Since then I've altered the shielding on the USB cable and I don't get any dropouts or lockups, even on jobs taking 12+ hours.