System.IO.Ports.SerialPort("COM23", 9600, Parity.None, 8, StopBits.One)
On some versions of Windows, in some software, using "COMnn" as the port name does not work. "COMn" does (a single digit). Why are there so many COM ports on your system? Mine has never used a number higher than 8.
Search the forum (the old one, especially) for "COM port above 9" to see how to use port names with numbers greater than 9. It involves some ridiculous combination of periods and slashes. See if that helps.