diff --git a/FlyleafLib/Controls/WPF/FlyleafWindow.cs b/FlyleafLib/Controls/WPF/FlyleafWindow.cs
index fc343355..777940f9 100644
--- a/FlyleafLib/Controls/WPF/FlyleafWindow.cs
+++ b/FlyleafLib/Controls/WPF/FlyleafWindow.cs
@@ -98,6 +98,8 @@ void WFH_Loaded(object sender, RoutedEventArgs e)
         public void Wndhost_LocationChanged(object sender, EventArgs e)
         {
             //Console.WriteLine("Wndhost_LocationChanged");
+            if (WindowBack == null) return;
+
             var locationFromScreen  = windowsFormsHost.PointToScreen(_zeroPoint);
             var source              = PresentationSource.FromVisual(WindowBack);
             var targetPoints        = source.CompositionTarget.TransformFromDevice.Transform(locationFromScreen);
diff --git a/FlyleafLib/MediaPlayer/Player.cs b/FlyleafLib/MediaPlayer/Player.cs
index 33a7c09b..cfa8af1c 100644
--- a/FlyleafLib/MediaPlayer/Player.cs
+++ b/FlyleafLib/MediaPlayer/Player.cs
@@ -373,7 +373,7 @@ public void Open(StreamBase inputStream)
             else if (inputStream is AudioStream)
             {
                 Utils.EnsureThreadDone(tOpenAudio);
-                Session.CurAudioStream.InUse = false;
+                if (Session.CurAudioStream != null) Session.CurAudioStream.InUse = false;
                 if (Config.audio.Enabled == false) Config.audio.SetEnabled();
 
                 tOpenAudio = new Thread(() => { OpenAudio((AudioStream)inputStream); });
@@ -382,7 +382,7 @@ public void Open(StreamBase inputStream)
             else if (inputStream is SubtitlesStream)
             {
                 Utils.EnsureThreadDone(tOpenSubs);
-                Session.CurSubtitleStream.InUse = false;
+                if (Session.CurSubtitleStream != null) Session.CurSubtitleStream.InUse = false;
                 Session.SubsText = null; sFrame = null;
                 if (Config.subs.Enabled == false) Config.subs.SetEnabled();