Not Authorized (can't mount USB flash drive as normal user)

[Steven I Usdansky]

Cristoph:

PREFERRED="ck-launch-session /usr/bin/startlxde" causes X to fail. 

PREFERRED=ck-launch-session /usr/bin/startlxde starts my LXDE
session, but I still get the same Not Authorized error

The Not Authorized error also occurs when booting into runlevel 5.