Possibly just a faulty button on the key fob. Do you have a spare key you could try?
Many garages/auto electrician/locksmiths will have a "point and click" tester like this (copy and paste)
http://www.shop-com.co.uk/Draper_Expert_Key_Fob_And_Remote_Control_Tester-23052304-31032069-p+.xhtml?sourceid=309
or just buy your own.
If you are handy with a soldering iron it might be worth opening the key and looking for dry/broken joints.
vaux, October 2009
