Sometimes, when using i3wm I get this error when mounting a partition. But it works for other des like gnome/cinnamon.
Make sure polkit is installed.
Loosen the polkit permissions in your system to allow your normal user to mount devices by creating a file at /etc/polkit-1/localauthority/50-local.d/org.freedesktop.automount.plka (as root!) with the following content:
[Allow Unauthorized mounting/Unmounting]
Identity=unix-group:plugdev;cdrom
Action=org.freedesktop.udisks2.filesystem-*;org.freedesktop.udisks2.eject*
ResultAny=yes
ResultInactive=yes
ResultActive=yes
You can loosen the polkit permissions in your system to allow your normal user to mount devices by creating a file at /etc/polkit-1/localauthority/50-local.d/org.freedesktop.automount.plka (as root!) with the following content:
groups
If “plugdev” is not listed, then use:
# gpasswd -a USER plugdev
newgrp plugdev
http://forums.debian.net/viewtopic.php?f=10&t=126872&start=30#
