I too have almost the exact same issue - 3,000 hours of run time on this machine without issue and all the sudden the spindle has stopped working. Here is the text of my complete error:
Unknown word where unary operation could be , Block = DOSPINCW()
The PC doesn't have windows updates on, problem happened after running another job just fine and the second job the spindle refused to start. Ripped apart all the hardware thinking it was physical but it appears to be in Mach3 as I never found any hardware issues.