Forms :: Error In Calendar Binding And Form

Getting Error while running my form after including toolbar, calendar and alerts etc..I've created a library and then attached it..but unfortunately nothing special is going.. When I run my program, it first compile and then gives error. When I reach the error, there is this script..

PROCEDURE date_choosen IS
BEGIN
copy(to_char(date_lov.current_lov_date,'dd-mon-yyyy'), date_lov.date_lov_return_item);
go_item(date_lov.date_lov_return_item);
if date_lov.lov_auto_skip = TRUE then
next_item;
end if;
END;

And not moving further. I'm also attaching my this form here. I've to use the calendar on my other 45 forms.