AJAX modalpopup not working

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ASP.NET

Ajax

dear all

I downloaded ajax extender toolkit and using it in vb2008

i create a simple default form and used a button to show the pop up window .

But when i run the form and click on that button nothing happlens... Why?

how to show the ajax popup window on button click?

Below is our sample coding

<form id="form1" runat="server">

    <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <div>
     <asp:Button ID="BtnOkay" runat="server" Text="Button" />
     <asp:ModalPopupExtender ID="ModalPopupExtender1" runat="server"
    CancelControlID="BtnCancel" OkControlID="BtnOK"
    TargetControlID="BtnOkay"  PopupControlID="Panel1" BackgroundCssClass="ModalPopupBG">
    </asp:ModalPopupExtender>
    <asp:Panel ID="Panel1" Style="display: none;"  class="HellowWorldPopup" runat="server" Height="90px" Width="205px">
    this is model popup
    <asp:Button ID="BtnCancel" runat="server" Text="Button" />
    &nbsp;<asp:Button ID="BtnOK" runat="server" Text="Button" />
    </asp:Panel>
    </div>
</form>
</body>
</html>

AND below is my CSS

.ModalPopupBG

{
  background-color:#CCCCFF;
  -ms-filter: alpha(opacity=70);
  -ms-opacity:0.7;
}

.HellowWorldPopup
{
    min-width:200px;
    min-height:150px;
    background:white;
}

IS there should be a code to show the window?