Error when removing a TitleWindow via PopUpManager - flex4.5

Question

I am having issues to remove a PopUp form my application. In fact I have a title Window with a component in it. In the component I have a Button, which when clicked should remove the TitleWindow (the PopUp). I am getting the error :
TypeError: Error #1009: Cannot access a property or method of a null object reference.
My Title Window is as follows:
<?xml version="1.0" encoding="utf-8"?>
<s:TitleWindow xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx" left="10"
width="1366" height="768">
<fx:Declarations>
<!-- Place non-visual elements (e.g., services, value objects) here -->
</fx:Declarations>
<fx:Script>
<![CDATA[
import mx.managers.PopUpManager;
public function removeTitleWindow():void {
PopUpManager.removePopUp(this);
}
]]>
</fx:Script>
<s:VGroup width="100%" height="100%" horizontalAlign="left">
<comps:SearchEngine />
<comps:SearchResults />
</s:VGroup>
</s:TitleWindow>
My Component is as follows:
<?xml version="1.0" encoding="utf-8"?>
<s:Group xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx" width="400 " height="300">
<fx:Declarations>
</fx:Declarations>
<fx:Script>
<![CDATA[
]]>
</fx:Script>
<s:Button label="Cancel" click="parentApplication.parentApplication.removeTitleWindow()"/>
</s:VGroup>
</s:Group>
Can someone help me on this?
Thanks

Answer 1

Got it Mates :)
I tried using parentApplication or rather flexGlobals.top... It didnt work.
Hence I used parentDocument.methodName().
This solved the issue.