Index: /trunk/src/VBox/Main/src-server/SnapshotImpl.cpp
===================================================================
--- /trunk/src/VBox/Main/src-server/SnapshotImpl.cpp	(revision 64216)
+++ /trunk/src/VBox/Main/src-server/SnapshotImpl.cpp	(revision 64217)
@@ -3130,5 +3130,6 @@
                 // make sure that the diff image to be deleted has no parent,
                 // even in error cases (where the deparenting may be missing)
-                it->mpSource->i_deparent();
+                if (it->mpSource->i_getParent())
+                    it->mpSource->i_deparent();
                 it->mpSource->uninit();
             }