A 'Blocked Beam' message may be caused by having the incorrect front face case fitted to a sensor.

The Transmitter Sensor is identified by having just the one clear glass IR Emitter and the 'Activate' button on the circuit board. Ensure that the correct front face case (one clear window on the left) is fitted to the Transmitter.

The Receiver Sensor has black IR Sensor on either side of the circuit board. Ensure that the correct front face case (a clear window on each side) is fitted to the Receiver.