My remote keyfob stopped working two weeks ago. My other key (a flip key) worked fine so I thought it was the battery. Changed this and still had no joy
Tried coding it to the car using the manual, no difference
Took it to the dealers as i had two days left on my warranty. They tried re-coding it using their equipment....nope
They then said that sometimes they just stopped working and it costs £30 for a new unit (fortunately free for me due to the warranty).
If it still starts the car (the immobilser chip is ok) then it may just be that the remote unit has given up the ghost.