Created Unassigned: AjaxControlToolkit.HTMLEditor cannot handle Test AjaxControlToolkit.HTMLEditor [27664]

[ASPX]
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit.HTMLEditor" TagPrefix="cc1" %>

<a href="http://www.asp.net" title="ASP.NET Website">www.asp.net</a>

<div>
<asp:ScriptManager ID="ScriptManager1" runat="server" />
<cc1:Editor ID="Editor1" runat="server" Width="500px" Height="300px"/>
</div>

[C#]
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
Editor1.Content = HttpUtility.HtmlDecode("<p><span><h1>Test AjaxControlToolkit.HTMLEditor</h1></span></p>");

}
}

[Error]
Error "Microsoft JScript runtime error: Unable to get value of the property 'nodeType': object is null or undefined" when click "www.asp.net"


Please help.