ObjectDisposedException when closing SerialPort in .Net 2.0

Question

I have a C# windows forms application which communicates with a USB dongle via a COM port. I am using the SerialPort class in .Net 2.0 for communication, and the serial port object is open for the lifetime of the application. The application sends commands to the device and can also receive unsolicited data from the device.

My problem occurs when the form is closed - I get (randomly, unfortunately) an ObjectDisposedException when attempting to close the COM port. Here is the Windows stack trace:

System.ObjectDisposedException was unhandled


Message=Safe handle has been closed
  Source=System
  ObjectName=""
  StackTrace:
       at Microsoft.Win32.UnsafeNativeMethods.SetCommMask(SafeFileHandle hFile, Int32 dwEvtMask)
       at System.IO.Ports.SerialStream.Dispose(Boolean disposing)
       at System.IO.Ports.SerialStream.Finalize()
  InnerException: 

I have found posts from people with similar problems and have tried the workaround [here][1]

[1]: http://zachsaw.blogspot.com/2010/07/net-serialport-woes.html although that is for an IOException and did not stop the problem.

My Close() code is as follows:

        public void Close()
    {
        try
        {
            Console.WriteLine("******ComPort.Close - baseStream.Close*******");
            baseStream.Close();
        }
        catch (Exception ex)
        {
            Console.WriteLine("******ComPort.Close baseStream.Close raised exception: " + ex + "*******");
        }
        try
        {
            _onDataReceived = null;
            Console.WriteLine("******ComPort.Close - _serialPort.Close*******");
            _serialPort.Close();
        }
        catch (Exception ex)
        {
            Console.WriteLine("******ComPort.Close - _serialPort.Close raised exception: " + ex + "*******");
        }            
    }

My logging showed that execution never got beyond attempting to close the SerialPort's BaseStream (this is in the first try block), so I experimented with removing this line but the exception is still thrown periodically - the logging in the second try block appeared then the exception happened. Neither catch block catches the exception.

Any ideas?

UPDATE - adding full class:

    namespace My.Utilities
{
    public interface ISerialPortObserver
    {
        void SerialPortWriteException();
    }

    internal class ComPort : ISerialPort
    {
        private readonly ISerialPortObserver _observer;
        readonly SerialPort _serialPort;

        private DataReceivedDelegate _onDataReceived;
        public event DataReceivedDelegate OnDataReceived
        {
            add { lock (_dataReceivedLocker) { _onDataReceived += value; } }
            remove { lock (_dataReceivedLocker) { _onDataReceived -= value; } }            
        }

        private readonly object _dataReceivedLocker = new object();
        private readonly object _locker = new object();

        internal ComPort()
        {         
            _serialPort = new SerialPort { ReadTimeout = 10, WriteTimeout = 100, DtrEnable = true };
            _serialPort.DataReceived += DataReceived;
        }

        internal ComPort(ISerialPortObserver observer) : this()
        {
            _observer = observer;         
        }

        private void DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            DataReceivedDelegate temp = null;

            lock (_locker)
            {
                lock (_dataReceivedLocker)
                {
                    temp = _onDataReceived;
                }

                string dataReceived = string.Empty;
                var sp = (SerialPort) sender;

                try
                {
                    dataReceived = sp.ReadExisting();
                }
                catch (Exception ex)
                {
                    Logger.Log(TraceLevel.Error, "ComPort.DataReceived raised exception: " + ex);
                }

                if (null != temp && string.Empty != dataReceived)
                {
                    try
                    {
                        temp(dataReceived, TickProvider.GetTickCount());
                    }
                    catch (Exception ex)
                    {
                        Logger.Log(TraceLevel.Error, "ComPort.DataReceived raised exception calling handler: " + ex);
                    }
                }
            }
        }

        public string Port
        {
            set
            {
                try
                {
                    _serialPort.PortName = value;
                }
                catch (Exception ex)
                {
                    Logger.Log(TraceLevel.Error, "ComPort.Port raised exception: " + ex);
                }
            }
        }

        private System.IO.Stream comPortStream = null;
        public bool Open()
        {
            SetupSerialPortWithWorkaround();
            try
            {
                _serialPort.Open();
                comPortStream = _serialPort.BaseStream;
                return true;
            }
            catch (Exception ex)
            {
                Logger.Log(TraceLevel.Warning, "ComPort.Open raised exception: " + ex);
                return false;
            }
        }

        public bool IsOpen
        {
            get
            {
                SetupSerialPortWithWorkaround();
                try
                {
                    return _serialPort.IsOpen;
                }
                catch(Exception ex)
                {
                    Logger.Log(TraceLevel.Error, "ComPort.IsOpen raised exception: " + ex);
                }

                return false;
            }
        }

        internal virtual void SetupSerialPortWithWorkaround()
        {
            try
            {
                //http://zachsaw.blogspot.com/2010/07/net-serialport-woes.html
                // This class is meant to fix the problem in .Net that is causing the ObjectDisposedException.
                SerialPortFixer.Execute(_serialPort.PortName);
            }
            catch (Exception e)
            {
                Logger.Log(TraceLevel.Info, "Work around for .Net SerialPort object disposed exception failed with : " + e + " Will still attempt open port as normal");
            }
        }

        public void Close()
        {
            try
            {
                comPortStream.Close();
            }
            catch (Exception ex)
            {
                Logger.Log(TraceLevel.Error, "ComPortStream.Close raised exception: " + ex);
            }
            try
            {
                _onDataReceived = null;
                _serialPort.Close();
            }
            catch (Exception ex)
            {
                Logger.Log(TraceLevel.Error, "ComPort.Close raised exception: " + ex);
            }            
        }

        public void WriteData(string aData, DataReceivedDelegate handler)
        {
            try
            {
                OnDataReceived += handler;
                _serialPort.Write(aData + "\r\n");
            }
            catch (Exception ex)
            {
                Logger.Log(TraceLevel.Error, "ComPort.WriteData raised exception: " + ex);                

                if (null != _observer)
                {
                    _observer.SerialPortWriteException();
                }
            }
        }
    }    
}