Permission of setuid helper not correct

[Max]

Binary package hint: dbus

Today turning on my pc, gdm didn't show the users list, locking me out of my desktop.
the log point my attention to a setuid permission problem on dbus-daemon-launch-helper.

resintalling dbus fixed the problem.
i can't imagine the cause of this problem.
yesterday i didn't do any update, so what could have changed these permissions?
---

the gmd log shows the following:

** (process:1492): DEBUG: Greeter session pid=1492 display=:0.0 xauthority=/var/run/gdm/auth-for-gdm-8XRvzQ/database

(gnome-power-manager:1493): libupower-glib-WARNING **: Couldn't enumerate devices: The permission of the setuid helper is not correct
*** ERROR ***
TI:10:16:35 TH:0x13560a0 FI:gpm-engine.c FN:gpm_engine_coldplug_idle_cb,837
 - failed to get device list: The permission of the setuid helper is not correct
Traceback:
 gnome-power-manager() [0x41ab04]
 gnome-power-manager() [0x41926f]
 /lib/libglib-2.0.so.0(g_main_context_dispatch+0x1f2) [0x7fe544bd5342]
 /lib/libglib-2.0.so.0(+0x442a8) [0x7fe544bd92a8]
 /lib/libglib-2.0.so.0(g_main_loop_run+0x195) [0x7fe544bd97b5]
 gnome-power-manager() [0x40f4db]
 /lib/libc.so.6(__libc_start_main+0xfe) [0x7fe5445add8e]
 gnome-power-manager() [0x407ec9]
gdm-simple-greeter[1492]: Gtk-WARNING: /build/buildd/gtk+2.0-2.22.0/gtk/gtkwidget.c:5684: widget not within a GtkWindow
Avviso del window manager: Buggy client sent a _NET_ACTIVE_WINDOW message with a timestamp of 0 for 0xe00034 (Finestra d)
Avviso del window manager: meta_window_activate called by a pager with a 0 timestamp; the pager needs to be fixed.
Avviso del window manager: Buggy client sent a _NET_ACTIVE_WINDOW message with a timestamp of 0 for 0xe00034 (Finestra d)
Avviso del window manager: meta_window_activate called by a pager with a 0 timestamp; the pager needs to be fixed.
gnome-session[1425]: WARNING: Could not connect to ConsoleKit: Could not get owner of name 'org.freedesktop.ConsoleKit': no such name
gnome-session[1425]: WARNING: Could not connect to ConsoleKit: Could not get owner of name 'org.freedesktop.ConsoleKit': no such name
gnome-session[1425]: WARNING: Could not connect to ConsoleKit: Could not get owner of name 'org.freedesktop.ConsoleKit': no such name
Avviso del window manager: CurrentTime used to choose focus window; focus window may not be correct.
Avviso del window manager: Got a request to focus the no_focus_window with a timestamp of 0. This shouldn't happen!
gnome-settings-daemon: Fatal IO error 11 (Risorsa temporaneamente non disponibile) on X server :0.0.

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: dbus 1.4.0-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.35-24.42-generic 2.6.35.8
Uname: Linux 2.6.35-24-generic x86_64
Architecture: amd64
Date: Wed Jan 12 10:51:58 2011
InstallationMedia: Ubuntu 10.04 "Lucid Lynx" - Beta amd64 (20100318)
ProcEnviron:
 LANG=it_IT.utf8
 SHELL=/bin/bash
SourcePackage: dbus