In the last two weeks I have encountered a "Lamp Defective" message a few times. The message is intermitant. It comes on when I engage the brakes. After I shut off the car for a few minutes the message may not appear again for several times of running. Then a few days later the message appears again. Bad bulb? Why would it be intermittent? Bad connection? I have removed and reinstalled both stop light bulbs. When I am at home all stop light bulbs work. Suggestions?