When working with SerialPort in your MF app always make sure to register the event handler AFTER opening the port!

            com2 = new SerialPort(COMPorts.COM2, 9600, Parity.None, 8, StopBits.One);
            com2.Handshake = Handshake.None;
            com2.Open();
            // VERY IMPORTANT: DataReceived event must be hooked up after the port has been opened
            com2.DataReceived += new SerialDataReceivedEventHandler(com2_DataReceived);