I've switched away from the User Control and I'm now using a normal Windows
Form instead to try and anrrow down the possible error sources.

The issue is still the same though :(

Where are some an example of what I'm trying to do:
------------------------------------------------------------
// InitializeExBgw() is called in the form constructor.

private void InitializeExBgw()
{
           this.ExBgw = new ExtendedBackgroundWorker();

           this.ExBgw.DoWork += new DoWorkEventHandler(ExBgw_DoWork);
           this.ExBgw.RunWorkerCompleted += new
RunWorkerCompletedEventHandler(ExBgw_RunWorkerCompleted);
}

private void ExBgw_DoWork(object sender, DoWorkEventArgs e)
{
           ExtendedBackgroundWorker worker = sender as
ExtendedBackgroundWorker;

           SQLServerLocator locator = new SQLServerLocator(); // My own
class. Scans for SQL servers on the network.

           string[] servers = locator.GetServers();

           e.Result = (string[])alTemp.ToArray(typeof(string));
}

private void ExBgw_RunWorkerCompleted(object sender,
RunWorkerCompletedEventArgs e)
{
           string[] servers = new string[] { "" };
           
           if (e.Error != null)
           {
               MessageBox.Show(this.Init.GetLanguageMessageError(2, "\n\n",
e.Error.Message), "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
           }
           else if (e.Cancelled)
           {
           }
           else
           {
               if (e.Result != null)
               {
                   servers = (string[])e.Result;

                   // this part will produce the cross-thread error
                   foreach(string s in servers)
                   {
                            this.ComboBox1.Items.Add(s);
                   }                  
               }
           }

           // this however, does not produce the cross-thread error
           this.PictureBox1.Image = null;
}

private void btn_Search_SQLServers_Click(object sender, EventArgs e)
{
           this.PictureBox1.Image = "my_progress_gif_file.gif";

           this.ExBgw.RunWorkerAsync(null); // used to send an object with
it, but it's not used in this example, hence "null".
}
------------------------------------------------------

Why can I load an image into a PictureBox but not populate a ComboBox or set
the Text property on a Label for that matter in "ExBgw_RunWorkerCompleted" ???

This doesn't make sense to me...

/Aidal