hi anybody
i test the trial version of telerik controls, and in one of my test encounterd this problem pleas help me
to understand and solve it

I wanna add daynamically panel to panel bar and then add tree to panel
and use TreeNodeExpandMode.ServerSideCallBack;
for tree node
but i got this error messege
the target 'RadPanelBar1$i0$i0$tree1for the callback could not be found or did not implement icallbackeventhandler

this is my source code:

using  System;
using System.Data;
using System.Configuration;
 using System.Collections;
using System.Web;
using System.Web.Security;
 using System.Web.UI;
 using System.Web.UI.WebControls;
 using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using Telerik.Web.UI;
 
public partial class Default2 : System.Web.UI.Page
{
 
RadTreeView tree = null;
 protected void Page_Load(object sender, EventArgs e)
{
tree = new RadTreeView();
 tree.ID = "tree1";
 if (!IsPostBack && !IsCallback)
{
 tree.NodeExpand += new RadTreeViewEventHandler(tree_NodeExpand);
 RadTreeNode node = new RadTreeNode("Node1");
 node.ExpandMode = TreeNodeExpandMode.ServerSideCallBack;
 tree.Nodes.Add(node);
 tree.Nodes.Add(new RadTreeNode("Node2"));
  RadPanelItem Item = new RadPanelItem("Panel1");
 RadPanelBar1.Items.Add(Item);
 RadPanelBar1.Items[0].Items.Add(new RadPanelItem());
 RadPanelBar1.Items[0].Items[0].Controls.Add(tree);
}
}
void tree_NodeExpand(object sender, RadTreeNodeEventArgs e)
 {
string s = e.Node.Text;
}
}

html code:

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default2.aspx.cs" Inherits="Default2" %>
 
<%@ Register Assembly="Telerik.Web.UI" Namespace="Telerik.Web.UI" TagPrefix="telerik" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
 <head runat="server">
 <title>Untitled Page</title>
  </head>
  <body>
 <form id="form1" runat="server">
 <div>
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
 <telerik:radpanelbar id="RadPanelBar1" runat="server"></telerik:radpanelbar>
</div>
</form>
</body>
</html>

thanks in advancs