Try to change
myda = new SqlDataAdapter("Select * from Events where EventDate='" +Calendar1.SelectedDate.ToString()+ "'", mycn);
myda = new SqlDataAdapter("Select * from Events where EventDate='" +Calendar1.SelectedDate.ToString("s")+ "'", mycn);
Calendar1.SelectedDate.ToString() to Calendar1.SelectedDate.ToString("s");
The problem is that displaying a date/time and use it in a SQL statement is not the same. Displaying date/time with DateTime.ToString() uses the current CultureInfo for that thread/computer where the program runs.