Quoted from MMP:For the long opto issue, if you have recently switched to LEDs (at least this was the fix for my game) replace the 2 lamps near the upper opto with incandescent. For a quick test go underside with a nut driver if you don't want to pull everything off the topside, and just remove those bulbs to give it a try.
i had the same , bright led's interfear the long beam opto .