Requiredfield validator is not working for dropdownlist

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ASP.NET

Hi all,


Requiredfieldvalidator is not working for dropdownlist which is present in footer tamplate of gridview control in asp.net

my code is as follows:

<FooterTemplate>
                            <asp:DropDownList ID="ddlcustomer" runat="server" AppendDataBoundItems="true" DataSource='<%#GetCustomer() %>'
                                DataTextField="CustomerName" DataValueField="CusVenID" ValidationGroup ="FtrowValidation">
                                <asp:ListItem Value="-1">-Select-</asp:ListItem>
                            </asp:DropDownList>
                           <asp:RequiredFieldValidator ID="reqfvCustomerName" runat="server" InitialValue="0" ControlToValidate="ddlcustomer"
                                 ValidationGroup="FtrowValidation" ErrorMessage="select Customer"
                                Display="Dynamic" Text ="*"></asp:RequiredFieldValidator>

                        </FooterTemplate>

please advise me.