hi
Could be the battery in the fob or it could be the fob wants synchronizing, or it could be the fob has run its life span with all the use it gets. Try changing the battery and resynchronizing ( key in ignition to position 2 and press both buttons.....doors should lock then unlock). If its the fob that has gone its a main dealer rob of around £90-£130 unless you can find a car electronic shop that does them cheaper.
paul
June 2008