The most obvious issue here is that you have this code:
asp:CalendarExtender ID="CalendarExtender1" runat="server" DefaultView="Years"
FirstDayOfWeek="Saturday" Format="dd/MM/yyyy"
TargetControlID="TextBoxBirthDate" EndDate="1997-12-31"
StartDate="1980-01-01" SelectedDate="1994-01-01"
Well, your
EndDate
,
StartDate
and
SelectedDate
aren't in the format dd/MM/yyyy. Change them to this:
EndDate="31/12/1997" StartDate="01/01/1980" SelectedDate="01/01/1994"