DevExpress call back panel with ValidatorCalloutExtender

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DevExpress

ASP.NET4

Hi all I am using ASPxCallbackPanel along with ValidatorCalloutExtender as follows

<dx:ASPxCallbackPanel ID="cbpnlProductCode" runat="server" ClientInstanceName="clicbpnlProductCode" OnCallback="cbpnlProductCode_Callback">
                <PanelCollection>
                    <dx:PanelContent ID="pnlProductCode" runat="server">
                        <dx:ASPxTextBox ID="ASPxTextBoxProductCode" runat="server" AutoPostBack="false">
                            <ClientSideEvents TextChanged="function(s,e){clicbpnlProductCode.PerformCallback();}" />
                        </dx:ASPxTextBox>
                        <asp:RequiredFieldValidator ID="rfvProductCode" runat="server" ValidationGroup="vgProducts" Display="None"
                            ControlToValidate="ASPxTextBoxProductCode"></asp:RequiredFieldValidator>
                        <asp:ValidatorCalloutExtender ID="ValidatorCalloutExtender1" runat="server" TargetControlID="rfvProductCode"></asp:ValidatorCalloutExtender>
                    </dx:PanelContent>
                </PanelCollection>
            </dx:ASPxCallbackPanel>

But when ever texx change occurs I am getting an exception as Extender controls must be registered using RegisterExtenderControl() before calling RegisterScriptDescriptors().