Exception on trying to change the state in Flex 3 - actionscript-3

Question

I am trying to change the stage state to different state on click of a button. The problem is some times am getting exception as The supplied DisplayObject must be child of the caller.
Here is what am trying to do to change the state
this.currentState = 'fullScreen';
here this is a canvas.
Here is the MXML for the State fullscreen
<mx:State name="fullScreen">
<mx:RemoveChild target="{lstExpert}"/>
<mx:RemoveChild target="{screenToggle}"/>
<mx:AddChild relativeTo="{outContainer}" position="firstChild">
<mx:HBox id="topHeaderBox" horizontalAlign="left" verticalAlign="middle" width="98.5%" height="60"/>
</mx:AddChild>
<mx:AddChild relativeTo="{topHeaderBox}" position="firstChild" >
<mx:Label id="lblCourseName" width="100%" text="Name" color="#ffffff" fontFamily="Arial" fontSize="14" fontWeight="bold" height="20" />
</mx:AddChild>
<mx:AddChild target="{screenToggle}" relativeTo="{lblCourseName}" position="after" />
<mx:AddChild relativeTo="message" position="before">
<mx:Spacer id="Bar" height="5" width="2" />
</mx:AddChild>
</state>
What would be the mistake here?

Answer 1

You might want to bind the relativeTo property value of the last AddChild object. Meaning, to write it like this:
<mx:AddChild relativeTo="{message}" position="before">
Assuming you have an element with that id.
Hope this helps.