意外错误：mscorlib.dll中发生未处理的“System.Reflection.TargetInvocationException”类型异常

Question

我在Visual Studio 2013（C＃）上构建一个Windows窗体程序，它从串行端口（在我的例子中是Arduino）读取数据并用它来更改图片。 Arduino返回一个8位字符串0和1，表示要更改的图片。例如 - 如果字符串为10001001，则程序应更改第1版，第5版和第8张图片。该程序能够从串行端口（通过串行通信）获取正确的字符串，但是当我添加一个使图片发生变化的方法时，有时会给我这个错误：

  

未处理的类型＆＃39; System.Reflection.TargetInvocationException＆＃39;发生在mscorlib.dll

并指出Program.cs上的那一行：

Application.Run(new Form1());

（我的表单名称为＆＃34; form1.cs＆＃34;名称空间为serial_read）

这是程序的样子：

这是我的form1.cs代码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO.Ports;
using System.Threading;

namespace Serial_receive
{
public partial class Form1 : Form
{
    SerialPort serialPort1 = new SerialPort(); //Defines Serial Port

    public Form1()
    {
        InitializeComponent();

        serialPort1.BaudRate = 9600;
        serialPort1.DtrEnable = true;

        foreach (string port in SerialPort.GetPortNames()) {comboBox1.Items.Add(port);} //Gives a list of the available ports

        serialPort1.DataReceived += serialPort1_DataReceived;
    }

   private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
   {
       string line = serialPort1.ReadLine(); //The serial string
       this.BeginInvoke(new LineReceivedEvent(LineReceived), line);

   }
   private delegate void LineReceivedEvent(string line);

   //Change image to a different image
   private void changeColor(PictureBox ob, string line, int l) //ob = PictureBox, line = the serial string, l = number of PictureBox
   {
       if (int.Parse(line.Substring(l, 1)) == 1)
           ob.Image = Serial_receive.Properties.Resources.red;
   }

   private void LineReceived(string line)
   {
       label1.Text = line;

       changeColor(l1, line, 0); //Picture 1
       changeColor(l2, line, 1); //Picture 2
       changeColor(l3, line, 2); //Picture 3
       changeColor(l4, line, 3); //Picture 4
       changeColor(l5, line, 4); //Picture 5
       changeColor(l6, line, 5); //Picture 6
       changeColor(l7, line, 6); //Picture 7
       changeColor(l8, line, 7); //Picture 8

   }

   private void button1_Click(object sender, EventArgs e) //Start Button
   {
       serialPort1.PortName = comboBox1.Text.ToString();

       if (comboBox1.Text.ToString() == "Select Port... (Default: COM4)" || comboBox1.Text.ToString() == "")
            serialPort1.PortName = "COM4";
       serialPort1.Open();
       button1.Enabled = false;
   }
}

}

为什么我收到此错误的任何想法？我对C＃有点新意，并不知道问题是什么......