try this Link
AJAX-Control-Toolkit-Calendar-Extender.aspx[
^]
<ajaxToolkit:CalendarExtender ID="CalendarExtender1" runat="server" PopupPosition="Right" PopupButtonID="TextBox2"
TargetControlID="TextBox1">
</ajaxToolkit:CalendarExtender>
<ajaxToolkit:CalendarExtender ID="CalendarExtender2" runat="server" PopupPosition="Right" PopupButtonID="Image2"
TargetControlID="TextBox2" Format="dddd, MMMM dd, yyyy">
</ajaxToolkit:CalendarExtender>
You need to give popup button id like On click of textbox or any other Button on Click of which calendor will PopUp. PopupButtonID="TextBox2" Or PopupButtonID="Image2"