i am trying to display dropdown pop up calendar for gridview textbox... But after running code, it displays nothing just a text box

This is my ASP.net code where I am using ajax calendar toolkit i am also using script manager for this.....
<EditItemTemplate> <asp:TextBox ID="txt_podate" runat="server" ></asp:TextBox> <ajaxToolkit:CalendarExtender ID="txt_podate_CalendarExtender" runat="server" Enabled="True" TargetControlID="txt_podate"> </ajaxToolkit:CalendarExtender> </EditItemTemplate>
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