private void mouse_down(object sender, MouseEventArgs e)
    {
        Control ctrl = sender as Control;

        UnsafeNativeMethods2.ReleaseCapture(ctrl.Handle);
        this.Drag();     // put the form into drag mode.
    }
 public void Drag()
 {
     UnsafeNativeMethods2.DefWindowProc(this.Handle, UnsafeNativeMethods2.WM_SYSCOMMAND, (IntPtr)UnsafeNativeMethods2.MOUSE_MOVE, IntPtr.Zero);
 }