External SWF Loading

programming flash
1

I am currently working on a project which requires the use of Away3D. What I have done is created a main SWF which has the main menu then loads the content via external swf’s. I have created these SWF’s which have heavy use of of Away3D, and they run fine when played on their own, but when I tried to play them through the main SWF, Flash kicks up the error:

TypeError: Error #1009: Cannot access a property or method of a null object reference .
    at away3d.core.clip::Clipping/screen()
    at away3d.containers::View3D/clear()
    at away3d.containers::View3D/render()
    at WorldDoc/onEnterFrame()
TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at away3d.core.clip::Clipping/screen()
    at away3d.containers::View3D/clear()
    at away3d.containers::View3D/render()
    at WorldDoc/onEnterFrame(

Any idea on how to fix this?This error is repeated hundreds of times whil,e the movie is running in the output panel.
Harry.