Hello. I'm getting an error that does not make sense.

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

In my application, the UI thread fires off backgroundWorker1, which when almost complete fires off backgroundWorker2 and waits for it to complete. backgroundWorker1 waits for backgroundWorker2 to complete, before it completes. AutoResetEvent variables are used to flag when each of the workers complete. In backgroundWorker2_RunWorkerComplete a function is called that resets the form controls. It is in this ResetFormControls() function where the exception is thrown. I thought it was safe to modify form controls in the RunWorkerCompleted function. Both background workers are instantiated from the UI thread. Here is a greatly summarized version of what I am doing:

  AutoResetEvent evtProgrammingComplete_c = new AutoResetEvent(false);
  AutoResetEvent evtResetComplete_c = new AutoResetEvent(false);

  private void ResetFormControls()
  {
     toolStripProgressBar1.Enabled = false;
     toolStripProgressBar1.RightToLeftLayout = false;
     toolStripProgressBar1.Value = 0;

     buttonInit.Enabled = true;
     buttonOpenFile.Enabled = true; // Error occurs here.
     buttonProgram.Enabled = true;
     buttonAbort.Enabled = false;
     buttonReset.Enabled = true;
     checkBoxPeripheryModule.Enabled = true;
     checkBoxVerbose.Enabled = true;
     comboBoxComPort.Enabled = true;
     groupBoxToolSettings.Enabled = true;
     groupBoxNodeSettings.Enabled = true;
  }

  private void buttonProgram_Click(object sender, EventArgs e)
  {
     while (backgroundWorkerProgram.IsBusy)
        backgroundWorkerProgram.CancelAsync();

     backgroundWorkerProgram.RunWorkerAsync();
  }

  private void backgroundWorkerProgram_DoWork(object sender, DoWorkEventArgs e)
  {
     // Does a bunch of stuff...

     if (tProgramStat_c == eProgramStat_t.DONE)
     {
        tProgramStat_c = eProgramStat_t.RESETTING;

        while (backgroundWorkerReset.IsBusy)
           backgroundWorkerReset.CancelAsync();

        backgroundWorkerReset.RunWorkerAsync();
        evtResetComplete_c.WaitOne(LONG_ACK_WAIT * 2);

        if (tResetStat_c == eResetStat_t.COMPLETED)
           tProgramStat_c = eProgramStat_t.DONE;
     }
  }

  private void backgroundWorkerProgram_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
  {
     // Updates form to report complete.  No problems here.

     evtProgrammingComplete_c.Set();
     backgroundWorkerProgram.Dispose();
  }

  private void backgroundWorkerReset_DoWork(object sender, DoWorkEventArgs e)
  {
     // Does a bunch of stuff...

     if (tResetStat_c == eResetStat_t.COMPLETED)
        if (tProgramStat_c == eProgramStat_t.RESETTING)
           evtProgrammingComplete_c.WaitOne();
  }

  private void backgroundWorkerReset_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
  {
     CloseAllComms();
     ResetFormControls();
     evtResetComplete_c.Set();
     backgroundWorkerReset.Dispose();
  }

Any thoughts or suggestions you may have would be appreciated. I am using Microsoft Visual C# 2008 Express Edition. Thanks.