C#

// constants for menu manipulation
const int SC_CLOSE = 0xF060;
const int MF_BYCOMMAND = 0x0;

[System.Runtime.InteropServices.DllImport("user32.dll")]
public static extern IntPtr RemoveMenu(IntPtr menuHwnd, int position, int flags );

[System.Runtime.InteropServices.DllImport("user32.dll")]
public static extern IntPtr GetSystemMenu(IntPtr hwnd, int bRevert);

public static void EnableApplicationClose( System.Windows.Forms.Form form, bool val )
{
	IntPtr menu = GetSystemMenu( form.Handle, val ? 1 : 0 );
	if ( !val && menu != IntPtr.Zero )
		RemoveMenu( menu, SC_CLOSE, MF_BYCOMMAND );
	else
	{
		// needed when enabling the app close box to force it to redraw.
		form.Enabled = false;
		form.Enabled = true;
	}
}

static bool IsDateTimeOk(string input)
{
	try
	{
		int year = int.Parse(input.Substring(0, 2)) + 2000;
		int month = int.Parse(input.Substring(2, 2));
		int day = int.Parse(input.Substring(4, 2));
		int maxDaysInFeb = 28;

		if(year % 4 == 0 && year % 100 != 0 && year % 400 == 0)
			maxDaysInFeb = 29;

		if(month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 ||	month == 12)
			if(day >= 1 && day <= 31)
				return true;
			else if(month != 2)
				if(day >= 1 && day <= 30)
					return true;
				else
					if(day >= 1 && day <= maxDaysInFeb)
					return true;

		return false;
	}
	catch
	{
		return false;
	}
}