Hi Brett, I know this may seem strange but I had a similar problem see "limit switch activated triggered" after countless contact with Mach forum members I thought I had solved the problem HOWEVER!!!
This aproblem started 3 months ago when the machine stopped halfway thru a program saying limit switch triggered, I restarted and all was fine, however this got worse finally it would take 10 or more attempts before I could cancel the triggers, (again the diagnostic did not show errors). Finally after getting the machine started I worked all day on jobs with no problem. Switched off the machine and the computer but realised I had one more to do. The computer would not start. After investigations it turned out the computers power supply had blown, so bought another power supply, put it in the computer and all was fine. 3 days later the error started again " limit switch triggered" then guess what the power supply failed again. So bought a secondhand Dell Optiplex computer "because it had the printer port outlet" low and behold Mach3 has been working fine ever since with no trigger signals (fingers crossed). Guess what I'm saying is if all fails and you checked your machines earthing is good and you cant sort out the problem it might not be Mach or your machine it could be your computer. I don't think any upgrades in Mach are the problem as my initial problem was with a system I had been using for 4 years. I suspect there is a rogue signal from your computer, it turned out my old computer had a motherboard intermitten fault which caused the power supply to fail. I bought an old computer on ebay for a tenner and solved the problem. Good Luck, Jim