Image sharing code not working for WP8 Plugin

The following code to save image and share it on social networks (whatsapp,facebook etc) works on the windows phone native app but not when used in unity windows phone 8 plugin

   public void SaveToLibraryAndShare() {
             MediaLibrary library = new MediaLibrary();
             Stream toShare = Application.GetResourceStream(new Uri(@"wallpaper/CustomizedPersonalWalleper_11.jpg", UriKind.Relative)).Stream;
             Picture picture = library.SavePicture("Memefy_Photo", toShare);
             var task = new ShareMediaTask();
             task.FilePath = picture.GetPath() ;
             task.Show();
         }

I have tried bringing the sharemediatask on the main thread using

  Deployment.Current.Dispatcher.BeginInvoke(() =>
             task.Show());

But this also crashes my unity app . What's the fix