Question About asp.net

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Hello I am developing one application in that I take gridview in page,i generated the dynamic textbox and I bind the calender extender through coding,but it did not work help me

the design code is following

 <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
                    BackColor="#DEBA84" BorderColor="#DEBA84" BorderStyle="None" BorderWidth="1px"
                    CellPadding="3" CellSpacing="2"
                    onselectedindexchanging="GridView1_SelectedIndexChanging"
                    DataKeyNames="event_id"
                    onselectedindexchanged="GridView1_SelectedIndexChanged"
                    onrowupdating="GridView1_RowUpdating" onrowediting="GridView1_RowEditing">
                    <RowStyle BackColor="#FFF7E7" ForeColor="#8C4510" />
                <Columns>
                    <asp:TemplateField>
                    &lt;HeaderTemplate>
                    Event Id
                    &lt;/HeaderTemplate>
                    <ItemTemplate>
                    <asp:Label ID="lbl1" Text='<%#Eval("event_id") %>' runat="server">
                    </asp:Label></ItemTemplate></asp:TemplateField>
                    <asp:TemplateField>
                    &lt;HeaderTemplate>
                    Event name
                    &lt;/HeaderTemplate>
                    <ItemTemplate>
                    <asp:Label ID="lbl" Text='<%#Eval("event_name") %>' runat="server">
                    </asp:Label></ItemTemplate></asp:TemplateField>
                    <%--<asp:TemplateField HeaderText="Event time">
                        <ItemTemplate>
                            <asp:Label ID="Label1" runat="server" Text='<%#Eval("event_date") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>--%>
                    <asp:BoundField DataField="event_date" HeaderText="Event Date" />
                    <asp:CommandField ShowEditButton="True" />
                    <asp:CommandField ShowDeleteButton="True" />
                </Columns>
                    <FooterStyle BackColor="#F7DFB5" ForeColor="#8C4510" />
                    <PagerStyle ForeColor="#8C4510" HorizontalAlign="Center" />
                    &lt;SelectedRowStyle BackColor="#738A9C" Font-Bold="True" ForeColor="White" />
                    &lt;HeaderStyle BackColor="#A55129" Font-Bold="True" ForeColor="White" />
                </asp:GridView>






The coding is following

I add the namespace using AjaxControlToolkit;


TextBox txt_box=new TextBox();
        txt_box.ID="txt_date";
       //txt_box=(TextBox)GridView1.Rows[e.RowIndex].Cells[3].Controls[0];
     AjaxControlToolkit.CalendarExtender cal_date = new AjaxControlToolkit.CalendarExtender();
       cal_date.ID = "cal_date";
       cal_date.Format = "dd-mm-yyyy";
       cal_date.TargetControlID = txt_box.ID;
       GridView1.Controls.Add(txt_box);
       GridView1.Controls.Add(cal_date);