gnome-screensaver not working

[Cinquero]

nvidia dual-screen setup, two separate xorg displays.

mark@i5 ~ $ pidof gnome-screensaver
mark@i5 ~ $ gnome-screensaver

Gtk-CRITICAL **: gtk_style_context_get_property: assertion `priv->widget_path != NULL' failed

GLib-GObject-WARNING **: /build/buildd/glib2.0-2.31.16/./gobject/gtype.c:4205: type id `0' is invalid

GLib-GObject-WARNING **: can't peek value table for type `<invalid>' which is not currently referenced
Speicherzugriffsfehler (Speicherabzug geschrieben)

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: gnome-screensaver 3.2.1-0ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-16.25-generic 3.2.6
Uname: Linux 3.2.0-16-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 1.91-0ubuntu1
Architecture: amd64
Date: Sat Feb 18 19:10:20 2012
EcryptfsInUse: Yes
GnomeSessionIdleInhibited: No
GnomeSessionInhibitors: None
GsettingsGnomeSession:
 org.gnome.desktop.session idle-delay uint32 0
 org.gnome.desktop.session session-name 'ubuntu'
ProcEnviron:
 SHELL=/bin/bash
 PATH=(custom, user)
 LANG=de_DE.UTF-8
 LANGUAGE=de:en
SourcePackage: gnome-screensaver
UpgradeStatus: Upgraded to precise on 2012-02-12 (6 days ago)
WindowManager: »/desktop/gnome/session/required_components/windowmanager« wurde kein Wert zugewiesen