Rheem criterion RGDG, changed the board this summer to fix blower, the glow stick comes on, the gas lights in all chambers. The gas stays on for several seconds then shuts off. I have three LED's the two on the right are green and stay lit, except for the middle on which starts to blink after the furnace comes on and off several times. I assume that means it is locked out. The left one never lights up, and I have sanded the flame sensor.

Usually it is the flame sensor that causes this problem. You can apply flame to the flame sensor and measure the current with a meter designed for that purpose. That will tell you if the flame sensor is operating correctly OR you can just replace it since it is the cheapest part to replace first.