If when the door reverses to the open position the main light flashes 10 times it is a sensor problem. If the light doesn't flash it isn't the sensors. If the door is closing too far it will reverse when it hits the floor. If this is the case find the 'down limit' on the side of the motor unit and adjust it. Turning the control in the opposite direction of the arrow printed on the cover will cause the door not to travel quite so far. If the door is reversing in the middle of travel and no lights flash increase the 'down force' just a little. This control is found on the end of the unit where all those white wires go.