my ajax control not works

Question

<form id="form1" runat="server">

    <asp:ScriptManager ID="ScriptManager1" runat="server">

    </asp:ScriptManager>

    <asp:TextBox ID="TextBox1" Columns="80" Rows="20" TextMode="MultiLine" runat="server"></asp:TextBox>

    <asp:HtmlEditorExtender ID="HtmlEditorExtender1" TargetControlID="TextBox1" EnableSanitization="false" runat="server">

    </asp:HtmlEditorExtender>

    </form>


it is my code afte viewbrowser it shows only the textbox with 80 20 


htmleditor extender doesnot shows on it

i use vs studio 2010 in frame work of 4.0.3


thanks advance