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

Using Thread:

  // Create a thread  
       Thread newWindowThread = new Thread(new ThreadStart(() =>  
       {  
         // You can use your code  
         // 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();  

Using Task and Thread:

 // Creating Task Pool, Each task will work asyn and as an indivisual thread component  
       Task[] tasks = new Task[3];  
       // Control drug data disc UI load optimize   
       tasks[0] = Task.Run(() =>  
       {  
         //This will handle the ui thread :The calling thread must be STA, because many UI components require this  
         TaskCompletionSource<object> source = new TaskCompletionSource<object>();  
         Thread thread = new Thread(() =>  
         {  
           try  
           {  
             GlobalVar.DrugCtrlDataDiskAsapVW = new DrugCtrlDataDiskAsap(string.Empty);  
             source.SetResult(null);  
           }  
           catch (Exception ex)  
           {  
             source.SetException(ex);  
           }  
         });  
         thread.SetApartmentState(ApartmentState.STA);  
         thread.IsBackground = true;  
         thread.Start();  
         return source.Task;  
       });  
       // Optimize report load for first time loading  
       tasks[1] = Task.Run(() =>  
       {  
         //This will handle the ui thread :The calling thread must be STA, because many UI components require this  
         TaskCompletionSource<object> source = new TaskCompletionSource<object>();  
         Thread thread = new Thread(() =>  
         {  
           try  
           {  
             VMPrintRxLabel printRxLabel = new VMPrintRxLabel();  
             printRxLabel.DummyReport();  
             source.SetResult(null);  
           }  
           catch (Exception ex)  
           {  
             source.SetException(ex);  
           }  
         });  
         thread.SetApartmentState(ApartmentState.STA);  
         thread.IsBackground = true;  
         thread.Start();  
         return source.Task;  
       });