Does it have an aftermarket alarm or remote starter installed? If so, it's probably not connected properly, and/or the locking/unlocking circuits aren't compatible.
Locking and unlocking are controlled by the Smart Junction Box. The wiring to the switches is all logic-level, low-current wiring, and it's highly reliable.
__________________   2007 Ford Edge SEL + AWD, Blazing Copper Metallic, Charcoal leather
* Navigation, Vista Roof, all factory options 2008 Ford Fusion SE FWD, Black Clearcoat, Charcoal/Red leather
* Sync, Sport Appearance Package Escape City | Edge Central | 
