CrossThreadMessagingException while using backgroundworker windows forms

I have a windows form application and have a button which calls a function

I am copying large files from one place to another.

It is taking a long time so I decided to use a progress bar. I need to invoke the Background process from the button click

The copyItems() function iterates through the list items and copies the items from another place. It in turn calls a function CopyListItem which copies one item .

I set a textbox value in the UI but it returns an An **exception 'Microsoft.VisualStudio.Debugger.Runtime.CrossThreadMessagingException' occurred**

How do I invoke the copy function in the backgroundworker todo event When I call the runworkerasync method in the click event I get an error

    private void btnCopyItems_Click(object sender, EventArgs e)
        {

            backgroundWorker1.RunWorkerAsync();
        }

I created a class


public partial class WorkerItem
    {

         Helper Helper = new Helper();
        Complaints comp = new Complaints();
        public void CopyItem(SPListItem sourceItem, string destinationListName, string destServerURL)
        {
            //Copy sourceItem to destinationList
            try
            {

               // copies file from one location to another

            }
            catch (Exception ex)
            {
                Helper.LogtoList("Copy List ", string.Format("  {0} Message {1} Source {2} Stack trace {3}", ex.InnerException.ToString(), "Message " + ex.Message + "Source" + ex.Source + "Stack trace" + ex.StackTrace));
            }

        }

    }

  private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            progressBar1.Value = e.ProgressPercentage;
                this.Text=e.ProgressPercentage.ToString();
        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
             try
            {
                  WorkerItem workerItem = (WorkerItem)e.Argument;

               // check if the site valid
                Helper.siteName = txtSite.Text;

                  progressBar1.Maximum = itemscoll.Count;
                  foreach (SPListItem sourceItem in itemscoll)
                      {
                         date = sourceItem["Date_x0020_Created"].ToString();
                         if (!string.IsNullOrEmpty(date))
                           {                               
                            workerItem.CopyItem(sourceItem, Helper.destinationListName, Helper.destServerURL);
                           }
                      }
                 }

                   Cursor.Current = Cursors.Default;
                   MessageBox.Show(string.Format("Items Copied {0}", Helper.ItemsCopied.ToString()));

            }
             catch (Exception ex)
             {

                 Helper.LogtoList("Main Function ", string.Format("{0} Message {1} Source {2} Stack trace {3}", ex.InnerException.ToString(), "Message " + ex.Message + "Source" + ex.Source + "Stack trace" + ex.StackTrace));

             }

        }