Javascript не видит PageMethods

  <form id="form1" runat="server"> 
 
     <div> 
         <asp:Button ID="Button1" runat="server" 
                Text="Test JS" OnClientClick="alertMe()" /> 
    </div>   
        <asp:ScriptManager ID="ScriptManager1"  
               runat="server" EnablePageMethods="true"> 
        </asp:ScriptManager> 
        <script type="text/javascript"> 
         function alertMe() 
         {                
             PageMethods.TestShow(OnSuccess); 
         } 
         function OnSuccess(response) 
         { 
             alert(response); 
         } 
    </script>