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>