Make sure the photo eyes are properly aligned. They will be either mounted on your vertical tracks or just to the left or right of the tracks. On that model you should have one that glows a bright orange or some say yellow and the other one should be green. If the orange eye is not on you could possibly have a bad circuit board and or photo eye. If it is orange and the other one is not green or is fluttering go over and loosen the screw and play with it until it glows a solid green. That unit is anywhere from 2-10 or 11 years old. I am not sure when they started using that frequency, but I know they just changed it again about 2 years ago.