Hi Please do this, it will work
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<cc1:CalendarExtender ID="CalendarExtender1" runat="server"
TargetControlID="TextBox1">
</cc1:CalendarExtender>
For More help see the tutorials at
http://www.asp.net/ajaxlibrary/act_Calendar_Simple.ashx[
^]
Regards,
Jojo Lili