I have set a property across threads before and I found this post http://stackoverflow.com/questions/142003/cross-thread-operation-not-valid-control-accessed-from-a-thread-other-than-the-t about getting a property.

I think my issue with the code below is setting the variable to the collection is an object therefore on the heap and therefore is just creating a pointer to the same object

So my question is besides creating a deep copy, or copying the collection into a different List object is there a better way to do the following to aviod the error during the for loop.

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

Code:

    private void btnRunProcess_Click(object sender, EventArgs e)
    {
        richTextBox1.Clear();

        BackgroundWorker bg = new BackgroundWorker();
        bg.DoWork += new DoWorkEventHandler(bg_DoWork);
        bg.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bg_RunWorkerCompleted);
        bg.RunWorkerAsync(lstProcessFiles.SelectedItems);
   }


    void bg_DoWork(object sender, DoWorkEventArgs e)
    {
        WorkflowEngine engine = new WorkflowEngine();
        ListBox.SelectedObjectCollection selectedCollection=null;

        if (lstProcessFiles.InvokeRequired)
        {
            // Try #1
            selectedCollection = (ListBox.SelectedObjectCollection) 
                this.Invoke(new GetSelectedItemsDelegate(GetSelectedItems), 
                new object[] { lstProcessFiles });

            // Try #2
            //lstProcessFiles.Invoke(
            //    new MethodInvoker(delegate {
            //        selectedCollection = lstProcessFiles.SelectedItems; }));
        }
        else
        {
            selectedCollection = lstProcessFiles.SelectedItems;
        }         

        // *********Same Error on this line********************
        // Cross-thread operation not valid: Control 'lstProcessFiles' accessed 
        // from a thread other than the thread it was created on.
        foreach (string l in selectedCollection)
        {
            if (engine.LoadProcessDocument(String.Format(@"C:\TestDirectory\{0}", l)))
            {
                try
                {
                    engine.Run();                       
                    WriteStep(String.Format("Ran {0} Succussfully", l));
                }
                catch
                {
                    WriteStep(String.Format("{0} Failed", l));
                }

                engine.PrintProcess();
                WriteStep(String.Format("Rrinted {0} to debug", l));
            }
        }
    }

    private delegate void WriteDelegate(string p);
    private delegate ListBox.SelectedObjectCollection GetSelectedItemsDelegate(ListBox list);

    private ListBox.SelectedObjectCollection GetSelectedItems(ListBox list)
    {
        return list.SelectedItems;
    }