Ajax里的控件HTMLEditor显示空白，急~

控件在设计时是可见的，在浏览器中却显示空白代码超简单
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default2.aspx.cs" Inherits="Default2" %>
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit.HTMLEditor"
    TagPrefix="cc1" %>
<!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></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:ScriptManager ID="ScriptManager1" runat="server" />
        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
            <ContentTemplate>
                <cc1:Editor ID="Editor1" runat="server" Height="300px" Width="600px" />
            </ContentTemplate>
        </asp:UpdatePanel>
    </div>
    </form>
</body>
</html>ajaxHTMLEditor