OldSoftLimitZ = GetSoftLimitForAxis(mc.Z_AXIS)

  OldSoftLimitZ = GetSoftLimitForAxis(mc.Z_AXIS))

One of these lines is not like the other..  In fact there is an extra ) on the last line. This will cause mach4 to instantly crash. this was in a m6 macro and caused me an hour or two of frustration to find. Running my m6 from the editor did not find this issue. I had to go through line by line to find this and when I did, I slapped my forehead.

btw, for those that care. This causes a divide by zero error in the mach4core.dll file. I found that by loading it into visual studio and running the program under the debugger.

This kind of bug shouldn't exist by now. it's been what, 10-12 years now with mach4. ( I was an early,early adopter)

Which build of Mach4 are you running?

that'd be build 5596 on a modified Industrial screenset.

You might need to update your Microsoft redistributable to 2022, I had an issue recently where I couldn’t debug anything in Zerobrane, updating this fixed it.

I can compile the code you posted above it it throws an error for me

This is what happens when I paste your code into the ZeroBrane editor and hit F7 (compile).

Compilation error on line 3:
untitled.lua:3: unexpected symbol near ')'
See the attached picture of the action in the ZeroBrane editor. 

When I edit code, I ALWAYS hit F7 before I save it and try to run it in Mach. 

I'm sorry, but bad script code is a killer.  You can ALWAYS crash Mach with bad LUA code.  We chose LUA because it was faster than anything else and the scripts run at near compiled C++ speed.  Unfortunately, with that speed comes the ability to crash because there is literally no protection layer.  You, the integrator, must be the protection layer.  Especially if you are doing something custom like a tool change script.  Zerobrane and F7 is your friend. 

Steve