Index: /trunk/src/VBox/Frontends/VirtualBox/src/medium/UIMediumEnumerator.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/medium/UIMediumEnumerator.cpp	(revision 50444)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/medium/UIMediumEnumerator.cpp	(revision 50445)
@@ -431,5 +431,9 @@
     /* Search for corresponding machine: */
     CMachine machine = vboxGlobal().virtualBox().FindMachine(strMachineID);
-    AssertReturnVoid(!machine.isNull());
+    if (machine.isNull())
+    {
+        /* Usually means the machine is already gone, not harmful. */
+        return;
+    }
 
     /* Calculate actual usage starting from root-snapshot if necessary: */