I have a Overhead garage door opener, Legacy Model 696CD/B. The garage door is stuck in the up position and will not close. The red sensor light flashes 3 times, pauses over and over. There is nothing obstructing the sensor and I switched the red sensor with the other door sensor and it works on the other door so it is not the other sensor. Any suggestions.

Not familiar with Legacy. Is there an electroinic lock option or button. With my Craftsman the light will flash but the door will not open if the "Lock" button has been pressed.