I've spent some time debugging this, and actually found a bug in the hamster-applet which triggers the behaviour described here. hamster-applet is watching all messages on the org.gnome.ScreenSaver interface, but doesn't handle them correctly, causing dbus to return an error even when the message is handled correctly by gnome-screensaver. See https://bugzilla.gnome.org/show_bug.cgi?id=600909
I've spent some time debugging this, and actually found a bug in the hamster-applet which triggers the behaviour described here. hamster-applet is watching all messages on the org.gnome. ScreenSaver interface, but doesn't handle them correctly, causing dbus to return an error even when the message is handled correctly by gnome-screensaver. See https:/ /bugzilla. gnome.org/ show_bug. cgi?id= 600909