串口未授权访问异常

我正在尝试从串行端口读取一些信息，但是当我实际打开连接时，它会引发未经授权的访问异常

此代码在端口名称中读取

        SerialPort port = new SerialPort();
        string[] serialPorts = System.IO.Ports.SerialPort.GetPortNames();

        public Page_Main()
        {
            InitializeComponent();
            for (int i = 0; i < serialPorts.Count(); i++)
                portBox.Items.Add(serialPorts[i]);
        }

这是尝试来自串行端口的信息的代码

            port.PortName = portBox.SelectedItem.ToString();
            port.BaudRate = 9600;
            port.DataBits = 8;
            port.Parity = Parity.None;
            port.StopBits = StopBits.One;
            port.Open();// This is where the exception is thrown
            serialOutput.Text = port.ReadLine();