Flash CS4 Professional - ActionScript 3.0 - External SWF loading

hi.. i developed application in action script 3.0 with adobe flash cs4 professional. In this application, i loaded another external swf which is having flash list component, but while loading the swf in main swf it showing TypeError: Error #1009: Cannot access a property or method of a null object reference.at fl.containers::BaseScrollPane/drawBackground()at fl.controls::List/draw()at fl.core::UIComponent/callLaterDispatcher() please, kindly suggest me for this issue.