I am having a problem loading a swf into a movieclip inside another swf. I keep getting this error message:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at contact_fla::MainTimeline/frame1()

after googling the error, I have come to suspect that I am trying to load the swf before the stage is ready for it. Although, I load another swf and it loads fine. How can I verify which part of my movie is causing the problem?