Index: /trunk/src/VBox/HostServices/SharedOpenGL/render/renderspu_wgl.c
===================================================================
--- /trunk/src/VBox/HostServices/SharedOpenGL/render/renderspu_wgl.c	(revision 43284)
+++ /trunk/src/VBox/HostServices/SharedOpenGL/render/renderspu_wgl.c	(revision 43285)
@@ -1128,5 +1128,13 @@
     /* Intel drivers require a window to be visible for proper 3D rendering,
      * so set it visible and handle the visibility with visible regions (see below) */
-    ShowWindow( window->hWnd, SW_SHOWNORMAL );
+    if (window->id)
+    {
+        ShowWindow( window->hWnd, SW_SHOWNORMAL );
+    }
+    else
+    {
+        CRASSERT(!showIt);
+        /* dummy window is always hidden in any way */
+    }
 
     //SetForegroundWindow( visual->hWnd );
@@ -1267,5 +1275,5 @@
              * various tables. This is hack which just hides the root case.
              */
-            crWarning("Recreating window in renderspu_SystemMakeCurrent\n");
+            crDebug("Recreating window in renderspu_SystemMakeCurrent\n");
             renderspu_SystemDestroyWindow( window );
             renderspu_SystemVBoxCreateWindow( context->visual, window->visible, window );