How to disable Previous Date in Aps.net Ajax Calender

to disable future date in Ajax calender use following code..this example only works in Ajax Calender extender Toolkit 4.0
just put this code on page load..to disable the all Future dates in Ajax calender extender

 
protected void Page_Load(object sender, EventArgs e)
{
AjaxCalendarExtender.EndDate = DateTime.Now;
}