yeah this happened to me a few weeks ago... same exact thing. you have to reprogram it to the car. the owner's manual will tell you exactly how to do it, but you basically stick the key in the ignition, turn it between position 1 and 3 (position 1 is just sticking the key in and turn it two clicks to get to position 3). you gotta cycle between position 1 and 3 like 8 times in 20 seconds and the car beeps at you. after that, you just have to press a button on the remote, and that should take care of it.
like i said - check the manual for precise instructions, but this fixed it for me.