Diagnosis
You need to perform a factory reset of the opener's memory. This erases all remote controls and keyless entry codes.
How to Fix It
Press and hold the learn button (yellow, under the light lens) for about 10 seconds. Release when the LED light next to it turns off. All previous codes are now cleared. The light will come back on solid.
If That Didn't Work
Some models require a slightly different sequence. Try holding the learn button for 6 seconds until the light blinks, then release and immediately press and hold it again for another 10 seconds until the light goes off.
Heads Up
This will also erase your wall console and keypad. You must re-program every device after the reset, including the wall console inside your garage.