.NET Error Closing serial port BaseStream error is only available when the port is open

I'm using the .NET System.IO.Ports.SerialPort using the BaseStream as suggested in this post If you must use .NET System.IO.Ports.SerialPort

But when I try to close the port or the baseStream, an System.InvalidOperationException is raised saying "The BaseStream is only available when the port is open"

This is my code:

      private void ActionStarted()
        {
            //ajusta el puerto
            setupSerial();

            serial.Open();  //conecta al plc
            byte[] buffer = new byte[15];
            Action kickoffRead = null;

            if (serial.IsOpen) //si esta abierto el puerto hace todo esto
            {
                kickoffRead = delegate()
                {
                    serial.BaseStream.BeginRead(buffer, 0, buffer.Length,
                        delegate(IAsyncResult ar)
                        {
                            try
                            {
                                int actualLength = serial.BaseStream.EndRead(ar);
                                byte[] received = new byte[actualLength];
                                Buffer.BlockCopy(buffer, 0, received, 0, actualLength);
                                raiseAppSerialDataEvent(received);
                            }
                            catch
                            {

                            }

                            kickoffRead();

                        }, null);
                };
                kickoffRead();
            }

        }

and the error occurrs when I try to close the window / port / basestream here, 

   private void Window_Closing(object sender, System.ComponentModel.CancelEventArgs e)
        {
            serial.BaseStream.Flush();
            serial.BaseStream.Close();
            serial.Close();
        }

I read somewhere that the serial port should be close on a different thread but I can't find that, so any thoughts??

Thanks!!