My 2005 taurus will not allow you to lock the driverside door with the power lock switch. When you remove the key from the ignition and open the door you here a chime which I think means the key is still in the ignition. Eventhough you have removed the key. While the chime is sounding if you try to use the power lock switch to lock the door it will lock and then unlock after a second or two. This problem is intermittent. When you dont hear the chime you can lock the door.