Often written in to the Ladder is a time out and a message will occur for M codes if the FIN(ish) confirmation signal is not seen.
IOW when an M code is issued, the control expects to see a FIN signal confirming the action has taken place or complete.
If the time out is not included, the system would just hang waiting for the FIN.
The signal can originate from a input via a L.S. or other means.
This sounds like the error you are getting?
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.