Vorrei bloccare la form soltanto cliccando un bottone e non ad ogni postback.

Utilizzo questo codice ma la form si blocca solo una volta, dove sbaglio ?


codice:
<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">

    <script src="Scripts/jquery-1.7.1.min.js" type="text/javascript"></script>
    <script src="Scripts/jquery.blockUI.js" type="text/javascript"></script>

   <script type="text/javascript">

       // unblock when ajax activity stops
       //              $(document).ajaxStop($.unblockUI);

     
      
      
       $(document).ready(function () {
           $('#Button1').click(function () {
               $.blockUI({ message: '<h1>[img]busy.gif[/img] Just a moment...</h1>' });

           });

         

           Sys.WebForms.PageRequestManager.getInstance().add_endRequest($.unblockUI);


//           // Get a reference to the PageRequestManager.
//           var prm = Sys.WebForms.PageRequestManager.getInstance();

//           prm.add_endRequest(function () {
//               // Unblock the form when a partial postback ends.
//               
//               $.unblockUI();
//           });



       });


       
 
</script> 



</asp:Content>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">

    <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <h2>
        ASP.NET
    </h2>
    


        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate>
        <asp:Button ID="Button1" runat="server" Text="Button" ClientIDMode="Static" 
                UseSubmitBehavior="False" />
        </ContentTemplate>
        </asp:UpdatePanel>

      <%--  <asp:Button ID="Button1" runat="server" Text="Button" ClientIDMode="Static" />--%>
        
    </p>
    


        È inoltre disponibile f="http://go.microsoft.com/fwlink/?LinkID=152368"
            title="MSDN ASP.NET Docs">documentazione relativa ad ASP.NET su MSDN</a>.
    </p>
</asp:Content>