Parameter child must be non-null / Help

Hope this will not be difficult to answer. Using CS5, AS3, and a bit of an AS noob. I’m getting this error (below) and I am unsure what it means and how to fix, specifically (Parameter child must be non-null). Any help will be appreciated.
Thanks so much.

TypeError: Error #2007: Parameter child must be non-null.
at flash.display::DisplayObjectContainer/removeChild()
at dvdheaderV01_TESTaCLEAN_fla::OilDrip_17/frame1()
at flash.display::MovieClip/gotoAndStop()
at dvdheaderV01_TESTaCLEAN_fla::MainTimeline/PL_LOADING()