UnauthorizedAccessException serialport

[kirkhettfield]

Hi, I have a problem with the UnauthorizedAccessException. Every time I
unplug=>plug my USB device, I get this exception. The problem is
that the exception is random so I cant track the source of it.

I can catch the exception, but it doesn't help because the program immediately shuts down.
CODE

public SerialPort moPort = new SerialPort();
public System.Timers.Timer timer6 = new System.Timers.Timer(1000);



void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
{
}

void moPort_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
delstring2 invoke_del = new delstring2(invoke_function);
try
{
this.Invoke(invoke_del, moPort.ReadLine());
kijken_gps_uitgetrokken = false;
}
catch
{
Longitude = "0";
kmperuur = 0;
direction = "0";
kwaliteit_signaal = "0";
kijken_gps_uitgetrokken = true;
}
}

public bool IsPortOpen()
{
//create vars for testing
bool _available = false;

//create a loop for each string in SerialPort.GetPortNames
foreach (string str in SerialPort.GetPortNames())
{
if (str == "COM3")
{
_available = true;
}
}

//return the temp bool
// Console.WriteLine("available " + _available);
return _available;
}

private void button1_Click(object sender, EventArgs e)
{
if (moPort.IsOpen == true)
{
moPort.DiscardInBuffer();
try
{
moPort.Close();
}
catch { }
button1.Text = "Connect";
comboBox1.Enabled = true;
textBox4.Enabled = true;
Console.WriteLine("timer1 gestopt");
}
else
{
moPort.PortName = "COM3";
moPort.BaudRate = 4800;
moPort.StopBits = System.IO.Ports.StopBits.One; //1
moPort.DataBits = 8;
moPort.Parity = System.IO.Ports.Parity.None;
try { moPort.Open(); }
catch { }
button1.Text = "Disconnect";
comboBox1.Enabled = false;
textBox4.Enabled = false;
timer6.Start();
}
}

void timer6_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
bool temp = IsPortOpen();
if (temp == false)
{
Console.WriteLine("com3 niet aanwezig");
try
{
moPort = null;
Console.WriteLine("Com poort disposed");
}
catch { }
else
{
try
{
Console.WriteLine("Com3 aanwezig");
moPort = new SerialPort();
moPort.PortName = "COM3";
moPort.BaudRate = 4800;
moPort.StopBits = System.IO.Ports.StopBits.One; //1
moPort.DataBits = 8;
moPort.Parity = System.IO.Ports.Parity.None;
moPort.Open();
Console.WriteLine("Com poort geopend");
}
catch { }
}
}