invalid application descriptor:descriptor version does not match runtime version

i have Air2 installed on my computer & i use Flex 4  ....

i have written below program whenever i compile main.mxml program with amxmlc main.swf file gets created

but when i run application descriptor program app.xml using adl i get the above error..please let me know a solution for this...

very soon as i m doing a project using AIR & Flex technologies....

Thank You...

file main.mxml:-

<?xml version="1.0" encoding="utf-8"?>

<s:WindowedApplication

     xmlms:fx="http://ns.adobe.com/mxml/2009"

     xmlns:s="library://ns.adobe.com/flex/spark"

     xmlms:mx="library://ns.adobe.com/flex/mx">

<fx:Script>

    <![CDATA[

              import mx.controls.Alert;

               public function clickHandler():void{

               Alert.show("Hello"+txtName.text);

        }

      ]]>

</fx:Script>

<s:TextInput id="txtName"/>

<s:Button label="Click Me!" click="clickHandler()"/>

</s:WindowedApplication>

file app.xml:-

<?xml version="1.0"  encoding="utf-8"?>

<application

  xmlns="http://ns.adobe.com/air/application/2.0">

   <id>Sample.helloName</id>

   <filename>helloName</filename>

    <version>1.0</version>

     <initialWindow>

   <content>main.swf</content>

</initialWindow>

</application>