I don't mean to resurrect such a long dead post, but i found a solution to a problem and want to post it in case anyone else has the same problem. Perhaps in a few years, someone will be running google searches and come across this thread like i did.
i have been plagued with this random "estop requested" error for quite awhile. Yesterday it pissed me off enough that i devoted half the day to fixing it.
I'm running mach3 with an ethernet smoothstepper, on a windows 7 machine on a G0704 conversion. I had tried ferrite beads all over pretty much everything (did nothing to help). I rerouted wires to keep high voltage away from low voltage wires (didn't work either). I set my various debounce settings in the smoothstepper plugin to as high as 200,000 (no effect whatsoever).
It started working fine after i deleted mach3 version 3.043.066 and installed version 3.043.062.
Suddenly, mysteriously, in the exact same machine with the same wiring, Mach 3 version 3.043.062 cured the random estop triggering.
My clue that it was a software issue and not a hardware issue was that it, in a 30,000 line program, it kept triggering the estop, on the exact same line of code. Every single time. I could reset the Estop, and "run from here", continuing from the same line of code and finish the program fine. but on many programs, it would trigger the estop, on the exact same line of code every single time i ran the program. Yesterday i ran the same program 10 times, and got the estop on that same line of code ( x 2.3, Y1.125, z-.125) Thats it, just a simple linear interpolation line amongst thousands of similar lines. but it estopped on that same line, every single time.