C#

Cross-thread operation not valid: Control 'lbConnections' accessed from a thread other than the thread it was created on.

using System;
using System.Text;
using System.Windows.Forms;
using System.Net.Sockets;

namespace UDP_Client
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            UdpClient udpClient = new UdpClient();
            udpClient.Connect(tbHost.Text, 8080);
            Byte[] sendBytes = Encoding.ASCII.GetBytes("Hello World?");
            udpClient.Send(sendBytes, sendBytes.Length);
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }
    }
}

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.Threading;
using System.Net;
using System.Net.Sockets;


namespace UDP_Server
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }


        public void serverThread()
        {
            UdpClient udpClient = new UdpClient(8080);
            while (true)
            {
                IPEndPoint RemoteIpEndPoint = new IPEndPoint(IPAddress.Any, 0);
                Byte[] receiveBytes = udpClient.Receive(ref RemoteIpEndPoint);
                string returnData = Encoding.ASCII.GetString(receiveBytes);
                lbConnections.Items.Add(RemoteIpEndPoint.Address.ToString() + ":" +
                returnData.ToString()
                );
            }
        }
        

        private void Form1_Load(object sender, EventArgs e)
        {

            Thread thdUDPServer = new Thread(new
                                    ThreadStart(serverThread));
            thdUDPServer.Start();
        }
    }
}

traceString = SeparateClass.TraceString;
traceFile.Write(traceString.ToString());
traceFile.Flush();
traceFile.Close()

testDomain.ProcessExit += delegate(object sender, EventArgs e)
{
  traceString = SeparateClass.TraceString;
  traceFile.Write(traceString.ToString());
  traceFile.Flush();
  traceFile.Close();
};