Does your spare key, one of 2 blue keys not work? This thread does not apply to cars with "Red" keys. First check that the batteries are not flat. Change the batteries with the working remote first without replacing. If they are dead replace(2x 3V lithium CR1220 about £5).
Then try the first reset in case the non working remote has been pressed 16+ times out of reception of car. Quickly press 2 times close to car and it should reset and open the car. If this does not work then check that this inoperative remote opens the car via manual door unlock with this key and that it then unimmobolises the car and starts it, If it does not then it is a matter of main dealer and reprogramming. If it has started the car then the following procedure will reprogramme the remote without the expensive call to the main dealer for reprogramming or "you need a new key" (£150+ and reprogramminig cost +£100 approx).
This information has kindly been provided by Nareman of Novola London, and it works.
The procedure for re-programming a spare key is as follows:
Using the working key, press the button to unlock the car, then press the same button to lock the car and continue to press the button to unlock and then lock the car, until the working key stops responding (it should take about 12-16 unlock/lock cycles for this to happen).
As soon as the working key stops responding, press the button on the non-working key and that key should then be reprogrammed to the car, including the original working key, leaving you with two functioning keys.
.........see how you go......report back.....
P