One problem I found was the timing of the pressing.

Open armrest, press button for 3 secs
turn ignition on (either posistion) Keep holding button
hold pressesd button for another 3 secs (not much longer) and let go. The screen then went to pairing.

One thing I was doing wrong was holding the buttton for a lot longer than 3 secs after turning the ignition on and it would not go to pairing. Now I count 3 to 4 flashes of the lights on the display.

Of course the system I have may be totally different to yours and I might be telling you rubbish as I am no expert but it works for me.

By the way mine is a late 2005 X5.

Good luck

John