Impliment treadpool in silverlight

Hi all

I am trying to speed up my silver light app which uses a web cam, as I don't like the way it displays a jittery display while processing an image

Up until now I have used a timer and processed an image every 250 m/s

let me try and explain with a bit of code

  public void StartTimer()
  {
   myDispatcherTimer.Interval = new TimeSpan(0, 0, 0, 0, 250);
   myDispatcherTimer.Tick += new EventHandler(Each_Tick);
   myDispatcherTimer.Start();
  } 

public void Each_Tick(object o, EventArgs sender)
{
    if (_captureSource.State == CaptureState.Started)
    {
      try
      {
        //Grab a frame from the stream
        ExtendedImage ExtImage = new ExtendedImage(WebcamCapture.ToImage());
        ProcessImage(ExtImage);
      }
      catch (Exception ex)
      {
        exception = ex;
      }
    }
}

So now what I want to do is to call the threadpool

public void Each_Tick(object o, EventArgs sender)
{
   ThreadPool.QueueUserWorkItem(new WaitCallback(myThread));
}

And define a new method like so:

public void myThread(object a)
{
    if (_captureSource.State == CaptureState.Started)
    {
     try
     {
       //Grab a frame from the stream
       ExtendedImage ExtImage = new ExtendedImage(WebcamCapture.ToImage());

       ProcessImage(ExtImage);
     }
     catch (Exception ex)
     {
       exception = ex;
     }
   }
}

But when I do this I'm getting an error “invalid cross thread access when using threadpool”

I've tried adding Thread.sleep at the end of the Thread method  but still dont work

Any Ideas as to how I can fix it