Ignore the on-screen message about a key not programmed. Continue to simultaneously press and hold the Mute and Select buttons until you see the two green lights flashing twice on the mode switch. Enter the code 11774.
If not working, try any of the ff codes.
11253 11601 10053 10160 10069
11633 11923 10731 11302 10169
10182 10650 10094 10683 10036
10463 11935* 10767* 11463*