Hi Lee thank you very much for the reply.

This is a problem I've had since purchasing the machine about 18 months ago and now has returned.
I have earth the VFD to the metal enclosure, and then taken a second earth from another suitable point in the enclosure to a mains earth.
I have also ran an earth for the main frame of the CNC again to a main earth.
I’ve tested the spindle body with main frame of the machine for continuity and that’s fine.

I’m not sure if i should completely uninstall Mach3 and reinstall.
I’m a little reluctant to use machine for any projects ata the moment just in case it crashes