Index: /trunk/src/VBox/Frontends/VirtualBox/src/medium/UIMedium.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/medium/UIMedium.cpp	(revision 44110)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/medium/UIMedium.cpp	(revision 44111)
@@ -202,4 +202,11 @@
             {
                 CMachine machine = vbox.FindMachine(*it);
+
+                /* UIMedium object can wrap newly created CMedium object which belongs to
+                 * not yet registered machine, like while creating VM clone.
+                 * We can skip such a machines in usage string.
+                 * CVirtualBox::FindMachine() will return null machine for such case. */
+                if (machine.isNull())
+                    continue;
 
                 QString sName = machine.GetName();