Anytime when the door is closing it reverses to the open position and the main light flashes 10 times it is a sensor problem. Most commonly the sensors are misaligned but it can also be a wiring problem. Each of the sensors has a small light that must be lit for them to operate properly. Tweak the sensors until those small lights are both lit and not flickering ever so slightly. If something (cat or dog or child) interrupts the invisible beam between the sensors when the door is open the light will come on and remain on for 4 1/2 minutes. The code that LED is blinking is "RPM sensor or motor overload" but the symptom you describe have nothing to do with this. I would just ignore that until you have dealt with the other problems. Please post back and let us know how you make out.

Don: I thought it was pretty clear in my first request but anyway, the sensors are in perfect alignment. The sending and receiving units' lights are lit solid. I even checked to make sure the wires were not shorted in some way. The blinking light on the back of the unit and the GDO light goming on and off by itself leads me to believe the problem is in the RPM sensor. My main concern is could there be a problem with one of the sensor units themselves (i.e. the receiving unit), or possibly a problem with the control circuit board. I hate to replace a lot of expensive parts and still not solve the problem. Thanks again.