Index: /trunk/src/VBox/Main/src-server/MediumImpl.cpp
===================================================================
--- /trunk/src/VBox/Main/src-server/MediumImpl.cpp	(revision 37624)
+++ /trunk/src/VBox/Main/src-server/MediumImpl.cpp	(revision 37625)
@@ -5684,5 +5684,6 @@
 
         // we must always have full paths now (if it refers to a file)
-        if (   (m->formatObj->getCapabilities() & MediumFormatCapabilities_File)
+        if (   (   m->formatObj.isNull()
+                || m->formatObj->getCapabilities() & MediumFormatCapabilities_File)
             && !RTPathStartsWithRoot(locationFull.c_str()))
             return setError(VBOX_E_FILE_ERROR,