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In your HAAS manual there is a section on ALARMS.
Checking a mill manual under X zero return margin too small. This is an error that occurs when the returned limit switch position is incorrect relative to the once per revolution mark on the lead screw. We have never had this error on any of our machines except when readjusting after having changed a cable.
Probably only requires a slight reposition of limit switch, or if the limit switch is a prox switch, then maybe there is contamination, a small metal chip, that causes an erroneous signal from the prox switch,