Index: /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UISession.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UISession.cpp	(revision 33755)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UISession.cpp	(revision 33756)
@@ -384,4 +384,9 @@
             if (rc != VBOX_E_NOT_SUPPORTED)
                 vboxProblem().cannotUpdateGuestAdditions(progressInstall, mainMachineWindow());
+
+            /* In every case we log the error message in the release log. */
+            QString strErr = progressInstall.GetErrorInfo().GetText();
+            if (!strErr.isEmpty())
+                LogRel(("%s\n", strErr.toLatin1().constData()));
             fDoMount = true; /* Since automatic updating failed, fall back to .ISO mounting. */
         }
Index: /trunk/src/VBox/Main/GuestImpl.cpp
===================================================================
--- /trunk/src/VBox/Main/GuestImpl.cpp	(revision 33755)
+++ /trunk/src/VBox/Main/GuestImpl.cpp	(revision 33756)
@@ -235,4 +235,6 @@
                 if (aTask->progress)
                     aTask->progress->SetCurrentOperationProgress(15);
+
+                LogRel(("Automatic update of Guest Additions started\n"));
 
                 /* Prepare command line args. */
@@ -285,4 +287,6 @@
                     else
                     {
+                        LogRel(("Copying Guest Additions installer to guest ...\n"));
+
                         if (aTask->progress)
                             aTask->progress->SetCurrentOperationProgress(20);
@@ -387,5 +391,5 @@
                 if (SUCCEEDED(rc))
                 {
-                    /* Nothing yet. */
+                    LogRel(("Executing Guest Additions update ...\n"));
                 }
             }