AJAX :: HTMLEditor Does Not Work?

I have a master page, aspx page, user control

I use HTMLEditor in the user control like this:

<HTMLEditor:Editor runat="server" ID="Editor" Height="300px" AutoFocus="true" Width="100%" />

in the code behind file

i use ((AjaxToolkitHtmlEditor.Editor)SettingsFormView.FindControl("Editor1")).Content. I got NULLReference Exception.

Also i use Editor editor = Page.FindControl("Editor") as Editor; still get null

my user control code is below:

<table width="100%"; style=" word-break:break-all">
<tr>
<td style="height:auto">
<HTMLEditor:Editor runat="server" ID="Editor" Height="300px" AutoFocus="true" Width="100%" />
<br />
<asp:ImageButton ID="add" runat="server" onclick="add_Click" ImageUrl="~/images/OK.gif" />
</td>
</tr>
</table>