The calling thread must be STA, because many UI components require this

Try to invoke your code from the dispatcher:

Application.Current.Dispatcher.Invoke((Action)delegate{      // your code});

If you make the call from the main thread, you must add the STAThread attribute to the Main method, as stated in the previous answer.

If you use a separate thread, it needs to be in a STA (single-threaded apartment), which is not the case for background worker threads. You have to create the thread yourself, like this:

Thread t = new Thread(ThreadProc);t.SetApartmentState(ApartmentState.STA);t.Start();

with ThreadProc being a delegate of type ThreadStart.

You can also try this

// create a thread  Thread newWindowThread = new Thread(new ThreadStart(() =>  {      // create and show the window    FaxImageLoad obj = new FaxImageLoad(destination);      obj.Show();          // start the Dispatcher processing      System.Windows.Threading.Dispatcher.Run();  }));  // set the apartment state  newWindowThread.SetApartmentState(ApartmentState.STA);  // make the thread a background thread  newWindowThread.IsBackground = true;  // start the thread  newWindowThread.Start();