alanm3sf

i tried using my "spare key" that i hardly ever use today, but it won't unlock/lock the car, nor can i start the car using it when plugged into ignition. the red light on the key lights up normal, and i replaced the battery to see if that was the cause, but no luck. what could this be? do i need to bring it to the dealer to reprogram? how much would this be?

thanks.

Alan