MX5 Key fob not working?

I have just bought a MK3 MX5 which came with two key remotes, one works perfectly the other one lights up when the buttons are pushed but nothing happens, I have replaced the battery but still nothing, can it be reprogrammed or is it a garage job or a new remote? any help would be most appreciated. the fob is the 4 button one.

John
June 2011