To fix this issue, add the following lines between <config …..> and </config> in /etc/PolicyKit/PolicyKit.conf
<match action="org.freedesktop.hal.storage.mount-removable"> <return result="yes"/> </match> <match action="org.freedesktop.hal.power-management.shutdown"> <return result="yes"/> </match> <match action="org.freedesktop.hal.power-management.reboot"> <return result="yes"/> </match>