This is a diagnostic feature which indicates that one of the keys is being read as down (always being pressed). In that condition, the CPU board will not be able to read any other keys. It can happen because of mechanical failure within the switch element, or keypad wires that are shorted to each other. The latter problem usually happens when insulation is scraped off some of the wires in the keypad cable as it's being pulled through the door frame. You may be able to restore operation by rapping on all the keys. If this works, however, it is likely only a temporary fix and you should be prepared to change the keypad. Next, check the wiring of the keypad cable into the board. If you don't see any problems, the keypad will need to be replaced but you can restore partial use, if you wish, while awaiting a replacement. Put the positive probe of a voltmeter on terminal WHT and successively apply the negative probe on terminals BLK, GRY, BRN, BGE, ORG, PNK, and VIO. "Good" terminals will read about 11 volts. Two terminals, however, will read about zero volts. Remove the wires from the two terminals which read zero volts. If you are wondering why a single down key does not create a single zero volt terminal read, you should understand that the keys are in a two of seven matrix so the one to one relationship doesn't hold. When you remove the two wires from the zero volt reading terminals, you will disable several keys. You will be able to determine which keys are working by pressing each key and seeing which ones are echoed by a beep and LED flash. You can then establish a temporary Hard code using only the active keys.