I've recently bought the 737NGX package. It is a really fantastic piece of work. I love the sounds and the realism in it. However I cannot get the aircraft to lock onto L-NAV. The moment I engage my cmd autopilot the aircraft starts rocking and then L-Nav disengages. I've read the tutorial and I do not know what I'm doing wrong. Its getting very frustrating. Any help or suggestions would be welcome. It is detracting from my enjoyment of what is a fantastic aircraft.