attachMovie from an external swf

Hello everyone, I have a pretty basic question.

I have 2 .swf : main.swf and child.swf

The main.swf load the movie with _root.myExternal.loadMovie(“child.swf”). Once everything is loaded I need to attach a movieClip from the child.swf to the main.swf.

In the child.swf, I tryed with _root.whatEverClipInMain.attachMovie(“myClip”,“myClipNewName”,_root.getNextHighestDepth());

And it wasn’t working. I’m wondering if we can attach a movieClip in a library top an other swf library?