Index: /trunk/src/VBox/Frontends/VBoxManage/VBoxManageStorageController.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VBoxManage/VBoxManageStorageController.cpp	(revision 44131)
+++ /trunk/src/VBox/Frontends/VBoxManage/VBoxManageStorageController.cpp	(revision 44132)
@@ -492,4 +492,6 @@
                                 CHECK_ERROR(pProperties, COMGETTER(DefaultAdditionsISO)(bstrIso.asOutParam()));
                                 strIso = Utf8Str(bstrIso);
+                                if (strIso.isEmpty())
+                                    throw Utf8Str("Cannot find the Guest Additions ISO image\n");
                                 pszMedium = strIso.c_str();
                                 if (devTypeRequested == DeviceType_Null)