private void pb_Visible(bool Visible)
        {
            try
            {
                if (this.InvokeRequired)
                    this.Invoke(d_pb_Visible, new object[] { Visible });
 
                else
                    pb.Visible = Visible;
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString(), "pb_Visible");
            }
        }