You have to implement some logic in DayRender event of calendar control so that it disables the past dates. Try the code as follows:
protected void Calendar1_DayRender(object sender, DayRenderEventArgs e)
{
if (e.Day.Date.CompareTo(DateTime.Today) < 0)
{
e.Day.IsSelectable = false;
}
}
Sometimes searching a solution is easier & faster than asking questions. :)
- DD