how to autogenerate serial no. in datagrid

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ASP.NET

Hi, i want to auto generate serial no . in data grid
I am using this code

<asp:DataGrid ID="dgdefaulertlist" runat="server" Width="85%" AutoGenerateColumns="false"
                   BackColor="White" BorderColor="#E7E7FF" BorderStyle="None" BorderWidth="1px" CellPadding="3" GridLines="Horizontal" AllowPaging="True" PageSize="40"  Height="10%"  OnPageIndexChanged="dgdefaulertlist_PageIndexChanged" AllowSorting="True" >
                   <Columns>
                       <asp:TemplateColumn HeaderText = "Serial No.">
                       <ItemTemplate>
                       <asp:Label ID = "lblserial" Text ='<%# Container.DataItemIndex + 1%>' runat= "server"></asp:Label>
                       </ItemTemplate>
                       </asp:TemplateColumn>
                    <asp:BoundColumn HeaderText="Date" DataField="startdate"></asp:BoundColumn>
                    <asp:BoundColumn HeaderText="Employee Name" DataField="employeename"></asp:BoundColumn>
                   </Columns>
                   <FooterStyle BackColor="#B5C7DE" ForeColor="#4A3C8C" />
                   <SelectedItemStyle BackColor="#738A9C" Font-Bold="True" ForeColor="#F7F7F7" />
                   <PagerStyle BackColor="#E7E7FF" ForeColor="#4A3C8C" HorizontalAlign="Right" Mode="NumericPages" />
                   <ItemStyle BackColor="#E7E7FF" ForeColor="#4A3C8C" />
                   <HeaderStyle BackColor="#4A3C8C" Font-Bold="True" ForeColor="#F7F7F7" />
                   <AlternatingItemStyle BackColor="#F7F7F7" />
               </asp:DataGrid>

it gives error
'System.Web.UI.WebControls.DataGridItem' does not contain a definition for 'DataItemIndex'

Thanks in Advance