I've been running the latest Mach3 release (R3.043.066) on Windows 7, with a UC100 USB to parallel controller, and a G540 (version eight), and I'm having an issue with a runaway axis (or two). I've had this happen to me infrequently in the past, maybe once every few months or so, but now it's happening every single time.
In the first video
https://www.youtube.com/watch?v=JjEN8x9O1Hg&feature=youtu.be you'll see a runaway X axis. I later reinstalled Mach3, and it appeared to have fixed things. Until it started again, this time about an hour into a CNC lathe setting up session, causing a Z axis runaway. I captured that in a second video
https://www.youtube.com/watch?v=L0cOSSliELU&feature=youtu.be.
The Gecko tech support said that their board could not be the one causing the issue, because it just reacts to the input signals. I tend to agree since the UC100 screen shows an active "Run" LED every time there's a runaway. The strange thing is that Mach3 DROs show no movement while the axis is running away, like it had nothing to do with it. Perhaps the UC100 is the issue. I have emailed them but so far no answer.
Has anyone ever run into this problem before?