How do i add admob ads in my app ?

[luke]

Steps that I have taken are listed below...

1) I have downloaded "admob for flash air (admob_all_in_o ne6.6.7.ane) from this link http://fuji.h1de.net/browse.php?u=Oi...zLw%3D%3D&b=13

2) I added this native extension to my flash cs6 project via advanced actionscript 3 settings -> library path tab.

3) Set my flash target to the air 4.0.01390 for android.

4) I wrote a small class to inialize add....

    package
    {
      import flash.display.Sprite;
	
	import so.cuo.platform.admob.Admob;
	import so.cuo.platform.admob.AdmobEvent;
	
	public class Interstitial extends Sprite
	{
		var admob:Admob= Admob.getInstance();
		
                public function Interstitial()
		{
		   super();
                }

                public function displayAdd():void
                {
		   if(admob.supportDevice)
                   {
                        // i have replaced setKeys with my admob ad unit id "ca-app-pub-xxxxxxxxxxx/xxxxxxxxxxx"
       			admob.setKeys("a152834c8723912"); 
                        
             	          admob.addEventListener(AdmobEvent.onInterstitialReceive,onAdReceived);
		        admob.cacheInterstitial();
		   }
		}

		protected function onAdReceived(event:AdmobEvent):void
		{
			if(event.type==AdmobEvent.onInterstitialReceive){
				admob.showInterstitial();
			}
		}
	}

5) In my main.as class I am calling the displayadd() method like this...

    var showAdd:Interstitial = new Interstitial();
    showAdd.displayAdd();

6) I have added this code to myappname-app.xml

    <android>
        <manifestAdditions>
           <![CDATA[<manifest>
               <uses-permission android:name="android.permission.INTERNET"/>
               <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
	       <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
                  <application>
		     <activity android:name="com.google.ads.AdActivity" android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|uiMode|screenSize|smallestScreenSize"/> 
		     </application>
           </manifest>]]>
        </manifestAdditions>
    </android>

    <extensions>
        <extensionID>so.cuo.platform.admob</extensionID>
     </extensions>

7) published app to my new samsung that uses andriod version 4.2.2

8) no ads display, my app just crashes and de-activates when i call

var showAdd:Interstitial = new Interstitial();
    showAdd.displayAdd();

have i missed something ?