DIAGNOSIS The infrared ice-full sensor is blocked or misaligned. It's a small plastic window inside the unit, opposite the ice chute.
FIX Unplug the machine. Remove the ice basket. Look for a small plastic lens or window on the side wall inside the cabinet. Wipe it clean with a dry, soft cloth. Remove any ice chips or dust. Also clear any ice shavings from the chute itself that could be blocking the beam.
IF THAT DIDN'T WORK The sensor itself may have failed. You can test it by shading the sensor with your hand when the basket is empty. If the 'Ice Full' light doesn't come on, the sensor is dead.
HEADS UP Don't stack ice above the 'Max' line in the basket. It can physically block the sensor and cause a false reading.