I have a problem with trackBar2 need help

[Chocolade]

The first problem is that i want to check if the variable file_info_trackBar2 is null or not.
So im checking if its null inside the StartWork function and if its null im doing trackBar2.Enable = false;

Now the backGroundWorking is starting to work and after few seconds file_info_trackBar2 isnt null.
So in the event: backGroundWorker1_DoWork im checking if file_info_trackBar2 isnt null != and its not so im doing trackBar2.Enable = true;
But i used a breakpoint on it and as its out after the trackBar2.Enable = true; im getting exception say:

Cross-thread operation not valid: Control 'trackBar2' accessed from a thread other than the thread it was created on

Whats that ? How can i solve it ? It happens only when im trying to make the trackBar2.Enable = true;

Second problem is inside the event: backGroundWorker1_DoWork again. I want that pb11 = new Bitmap(@"e:\radar003626.jpg"); instead this file it will make new Bitmap to the current file is on trackBar1. And in the function LoadPictureAt im getting the current file name on pictureBox1.Load(file_info_mouse_wheel[nIndex].FullName);
But how do i pass or use this file name on the pb11 = new Bitmap ?

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;
 
namespace WindowsFormsApplication1
{
    public partial class Picturebox1_Fullscreen : Form
    {
        int nIndex1;
        BackgroundWorker backGroundWorker1;
        Bitmap[] myBitmaps;
        Bitmap pb11;
        FileInfo[] file_info_mouse_wheel;
        string radar_images_download_directory;
        private Bitmap[] file_info_trackBar2;
        private bool _isDirty = false;
 
 
        public Picturebox1_Fullscreen()
        {
            InitializeComponent();
 
 
            backGroundWorker1 = new BackgroundWorker();
            backGroundWorker1.WorkerSupportsCancellation = true;
            backGroundWorker1.DoWork += new DoWorkEventHandler(backGroundWorker1_DoWork);
            backGroundWorker1.RunWorkerCompleted += new RunWorkerCompletedEventHandler(backGroundWorker1_RunWorkerCompleted);
 
            radar_images_download_directory = Options_DB.Get_Radar_Images_Download_Directory();
            DirectoryInfo dir1 = new DirectoryInfo(radar_images_download_directory);
            file_info_mouse_wheel = dir1.GetFiles("*.jpg");
            trackBar1.Minimum = 0;
            trackBar1.Maximum = file_info_mouse_wheel.Length - 1;
            trackBar1.Value = file_info_mouse_wheel.Length - 1;
 
            // To check the pb11 new.....and to check how to check the file_info_trackBar2 if it null what to do \\
 
         //   if (file_info_trackBar2 == null)
          //  {
            //    trackBar2.Enabled = false;
           // }
 
                StartWork();
            this.FormClosing += new FormClosingEventHandler(Picturebox1_Fullscreen_FormClosing);
 
 
        }
 
        private void splitContainer1_Panel1_DoubleClick(object sender, EventArgs e)
        {
            this.Close();
        }
 
        private void splitContainer1_Panel2_DoubleClick(object sender, EventArgs e)
        {
            this.Close();
        }
 
        private void pictureBox1_DoubleClick(object sender, EventArgs e)
        {
            this.Close();
 
        }
 
        private bool LoadPictureAt(int nIndex, object c)
        {
 
            bool bRet = false;
 
            if (nIndex >= 0 && nIndex < file_info_mouse_wheel.Length)
            {
                if (c.Equals(trackBar1))
 
                    pictureBox1.Load(file_info_mouse_wheel[nIndex].FullName);
                nIndex1 = nIndex;
                    bRet = true;
 
            }
            if (file_info_trackBar2 == null)
            {
            }
            else
            {
                if (nIndex >= 0 && nIndex < file_info_trackBar2.Length)
                {
                    if (c.Equals(trackBar2))
                        pictureBox1.Image = file_info_trackBar2[nIndex];
                    bRet = true;
                }
            }
            return bRet;
 
        }
 
        private void trackBar2_Scroll(object sender, EventArgs e)
        {
            StartWork();
            LoadPictureAt(trackBar2.Value, sender);
            pictureBox1.Refresh();
 
 
        }
 
        private void trackBar1_Scroll(object sender, EventArgs e)
        {
            LoadPictureAt(trackBar1.Value, sender);
        }
 
 
        public PictureBox picturebox1(PictureBox pb1)
        {
            pictureBox1.Image = pb1.Image;
            return pictureBox1;
        }
 
        public string picturebox1_lastFile(string last_file)
        {
            pictureBox1.Load(last_file);
            return last_file;
       }
 
        private void backGroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            int f = (int)e.Argument;
            pb11 = new Bitmap(@"e:\radar003626.jpg");
            myBitmaps = ImagesComparison.get_images_with_clouds(pb11);
            if (this.backGroundWorker1.CancellationPending)
            {
                e.Result = f;
                return;
            }
            file_info_trackBar2 = myBitmaps;
            e.Result = f;
            pb11.Dispose();
            if (file_info_trackBar2 != null)
            {
                trackBar2.Enabled = true;
            }
        }
 
 
 
        private void Picturebox1_Fullscreen_FormClosing(object sender, FormClosingEventArgs e)
        {
            //put in code here to show a message, or take some action
            //if the bgw isBusy
 
            if (backGroundWorker1 != null)
                backGroundWorker1.Dispose();
        }
 
        private void backGroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            //display result
 
            //if previous bgw-operation cancelled
            //start bgw again, so, that the current
            //result is the current trackbar-value
            if (this._isDirty)
            {
                this._isDirty = false;
                StartWork();
            }
        }
 
        private void StartWork()
        {
 
 
                //run bgw
                if (this.backGroundWorker1.IsBusy == false)
                {
                    this.backGroundWorker1.RunWorkerAsync(this.trackBar2.Value);
                    if (file_info_trackBar2 == null)
                    {
                        trackBar2.Enabled = false;
                    }
                }
                else
                {
                    //force re-run of bgw
                    this._isDirty = true;
                    //and cancel current action of bgw
                    this.backGroundWorker1.CancelAsync();
                }
 
        }
 
 
 
 
 
 
 
    }
}
 

Thanks for helping.