To Close Calendar in AJAXToolkit:CalendarExtender click

http://forums.asp.net/t/1067091.aspx?PageIndex=2

Step1: Write this in Master Page

function hideCalendar(oCalendar)
{
oCalendar.hide();
oCalendar.get_element().blur();
}

Step2: Include OnClientDateSelectionChanged="hideCalendar" in CalendarExtender AJAX