Haas Alarm: 921 (M) APC LOAD-SWITCH MISSED PAL 4 – Pallet #4 did not complete its move from the APC to the receiver in the allowable time. Pallet change sequence was halted because receiver switch was not activated. Pallet is either unclamped or not on the receiver. Ensure the pallet is correctly located on receiver (against hard stop), then run M18 to clamp the pallet. After correcting the condition, run M50 to continue machining.