C#, NULL com port

my C# program will not pick up the Null com port on a windows 2008 R@ Server, stand-alone. but this same code work on other computers... why ?

public Form1()
{

InitializeComponent()
_serialPort.DataReceived += new  SerialDataReceivedEventHandler(DataRecivedHandler);

foreach ( sting s in SerialPort.GetPortNames())
{
comport.Items.add(s);
}

}