ajax non of the controls works

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>

<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>     <asp:UpdatePanel ID="UpdatePanel1" runat="server">     <ContentTemplate>

  <asp:TextBox ID="TextBox1_cmbOpen" runat="server" Width="155px" Font-Size="Large"></asp:TextBox>

      <asp:MaskedEditExtender       runat="server"     TargetControlID="TextBox1_cmbOpen"     Mask="9,999,999.99"     MessageValidatorTip="true"         MaskType="Number"     InputDirection="RightToLeft"     AcceptNegative="Left"     DisplayMoney="Left"    ErrorTooltipEnabled="True"/>

 </ContentTemplate>      </asp:UpdatePanel>    

JavaScript runtime error: Unable to get property 'UI' of undefined or null reference