One of the keys for my Impreza 2002 model won't communicate with the remote transponder.

I believe that this can be fixed by reprogramming it via the ignition switch, but the owners handbook says this needs to be done by a dealer.

Has anyone done this themselves?

I'm not sure Actionman might have done some by now he does keys for other makes of cars. But I would have thought it would be a dealer job myself :( 

Thanks for the prompt response.

I dismantled the key and cleaned small amounts of green corrosion from the contacts.  Problem solved!

Result. And not a problem at all :) glad you got it sorted and cheap too ;)