Comment 5 for bug 312105

I have exactly the same problem, on two Jauntu boxes (up-to-date on 2009-03-02). On the box I'm currently using:

$ polkit-auth --show-obtainable
org.freedesktop.consolekit.system.stop-multiple-users
org.freedesktop.consolekit.system.restart-multiple-users
org.freedesktop.policykit.read
org.freedesktop.policykit.revoke
org.freedesktop.policykit.grant
org.freedesktop.policykit.modify-defaults
com.ubuntu.systemservice.setproxy
com.ubuntu.systemservice.setnoproxy
com.ubuntu.systemservice.setkeyboard
org.freedesktop.hal.device-access.modem
org.freedesktop.hal.device-access.ppdev
org.freedesktop.network-manager-settings.system.modify
org.gnome.clockapplet.mechanism.settimezone
org.gnome.clockapplet.mechanism.settime
org.gnome.clockapplet.mechanism.configurehwclock
org.freedesktop.hal.storage.mount-fixed
org.freedesktop.hal.storage.unmount-others
org.freedesktop.hal.storage.crypto-setup-fixed
com.ubuntu.screenresolution.mechanism.configure
com.ubuntu.screenresolution.mechanism.dontzap
org.gnome.cpufreqselector
org.freedesktop.systemtoolsbackends.set
org.freedesktop.systemtoolsbackends.self.set
org.gnome.gconf.defaults.set-system
org.gnome.gconf.defaults.set-mandatory
org.freedesktop.hal.power-management.shutdown-multiple-sessions
org.freedesktop.hal.power-management.reboot-multiple-sessions
com.ubuntu.devicedriver.install

$ ck-list-sessions
Session8:
 unix-user = '1000'
 realname = 'Dimitry Andric,,,'
 seat = 'Seat1'
 session-type = ''
 active = TRUE
 x11-display = ':0'
 x11-display-device = '/dev/tty7'
 display-device = ''
 remote-host-name = ''
 is-local = TRUE
 on-since = '2009-03-02T21:57:04.909821Z'
 login-session-id = '4294967295'