I believe there is a paragraph in the "starting the engine" section of the manual that mentions the immobilizer. It is an anti-theft device that prevents engine start unless a properly programmed key is used. There is a transponder chip in the key, an antenna around the ignition switch. If more than 1 key with chip is near the antenna, signal can be lost and no start. Could be problem with transponder, key, antenna, wiring, control unit, interference from some outside source. Only way to know is to have it diagnosed. Control module usually stores a fault code if there is a problem.