an ME81 is excess motor rotation. If it happens,and the car was at or near floor level, it most likely occurs during current ramp down. the drive holds the car in place until the brake sets. In this case the motor field current may have changed from when the car was setup, causing the car to pull through the brake, or the drive isn't strong enough to hold the car until the brake sets. Another thing he should check is the coupling on the position encoder, if it happens some where else in the hoist way.