Index: /trunk/src/VBox/Frontends/VirtualBox/src/medium/UIMediumEnumerator.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/medium/UIMediumEnumerator.cpp	(revision 59817)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/medium/UIMediumEnumerator.cpp	(revision 59818)
@@ -280,5 +280,9 @@
 
     /* Make sure such UIMedium still exists: */
-    AssertReturnVoid(m_mediums.contains(strUIMediumKey));
+    if (!m_mediums.contains(strUIMediumKey))
+    {
+        LogRel2(("GUI: UIMediumEnumerator: Medium with key={%s} already deleted by a third party\n", strUIMediumKey.toUtf8().constData()));
+        return;
+    }
 
     /* Check if UIMedium ID was changed: */