After update from 11.04 to 11.10 an wired conduct appears in my machine:

Shutdown GUI methods (including reboot) cause only a log off, and in the login screen, shutdown nor reboot options do anything (if you wonder, reboot appears in the shutdown dialog).

The only way i can reboot or shutdown is trough console sudo shutdown -h now or sudo reboot. This is OK for me, but not for the rest of the users.

How to fix this?

Update

The syslog output when select shutdown from my desktop is:

AptDaemon: INFO: Quitting due to inactivity
AptDaemon: INFO: Quitting was requested
CRON[5095]: (root) CMD (  [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) ! -execdir fuser -s {} 2>/dev/null \; -delete)
CRON[5094]: (root) MAIL (mailed 1 byte of output; but got status 0x00ff, #012)
kernel: [17027.614974] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
kernel: [17027.616510] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
kernel: [17027.618037] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
kernel: [17027.619557] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
kernel: [17027.621046] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
kernel: [17027.621051] psmouse.c: issuing reconnect request
acpid: client 1032[0:0] has disconnected
acpid: client connected from 1032[0:0]
acpid: 1 client rule loaded
gnome-session[1836]: WARNING: Unable to stop system: Authorization is required
acpid: client 1032[0:0] has disconnected
acpid: client connected from 6055[0:0]
acpid: 1 client rule loaded
rtkit-daemon[1313]: Successfully made thread 6134 of process 6134 (n/a) owned by '119' high priority at nice level -11.
rtkit-daemon[1313]: Supervising 4 threads of 2 processes of 2 users.
rtkit-daemon[1313]: Successfully made thread 6139 of process 6134 (n/a) owned by '119' RT at priority 5.
rtkit-daemon[1313]: Supervising 5 threads of 2 processes of 2 users.
rtkit-daemon[1313]: Successfully made thread 6140 of process 6134 (n/a) owned by '119' RT at priority 5.
rtkit-daemon[1313]: Supervising 6 threads of 2 processes of 2 users.

I suspect that the line gnome-session[1836]: WARNING: Unable to stop system: Authorization is required is related to the issue.

When selecting shutdown from the login screen, the output is the same from the line pointed. This is the output:

gnome-session[1836]: WARNING: Unable to stop system: Authorization is required
acpid: client 1032[0:0] has disconnected
acpid: client connected from 6055[0:0]
acpid: 1 client rule loaded
rtkit-daemon[1313]: Successfully made thread 6134 of process 6134 (n/a) owned by '119' high priority at nice level -11.
rtkit-daemon[1313]: Supervising 4 threads of 2 processes of 2 users.
rtkit-daemon[1313]: Successfully made thread 6139 of process 6134 (n/a) owned by '119' RT at priority 5.
rtkit-daemon[1313]: Supervising 5 threads of 2 processes of 2 users.
rtkit-daemon[1313]: Successfully made thread 6140 of process 6134 (n/a) owned by '119' RT at priority 5.
rtkit-daemon[1313]: Supervising 6 threads of 2 processes of 2 users.
acpid: client 6055[0:0] has disconnected
acpid: client connected from 6055[0:0]
acpid: 1 client rule loaded