missing start dates property calendarextender

I am using a calendarextenderas folllow

<asp:calendarextenderID="Cal3" TargetControlID="txtDate"runat="server">

</asp:calendarextender>

But the properties of Startdate and Enddate are not there.  The option to set these dates are not given.

if i add the StartDate anyway i get the error:

Type 'AjaxControlToolkit.CalendarExtender' does not have a public property named 'StartDate'

Any idea why??

Thank you