Index: /trunk/src/VBox/Main/src-server/MachineImpl.cpp
===================================================================
--- /trunk/src/VBox/Main/src-server/MachineImpl.cpp	(revision 54965)
+++ /trunk/src/VBox/Main/src-server/MachineImpl.cpp	(revision 54966)
@@ -14136,5 +14136,5 @@
         {
             mrc = setError(rc,
-                           tr("Locking of attached media failed"));
+                           tr("Locking of attached media failed. A possible reason is that one of the media is attached to a running VM"));
         }
     }