[flexcoders] The supplied DisplayObject must be a child of the caller

[jmfillman]

So I'm trying to remove a child from a canvas container.

trace (this.getChildAt(6));
this.removeChild(this.getChildAt(6));
this.removeChildAt(6);

The trace statement returns the path to the correct child, but when I try 
removeChild() or removeChildAt(), I get:

The supplied DisplayObject must be a child of the caller 
    at flash.display::DisplayObjectContainer/getChildIndex()

Why???