Comment 3 for bug 600575

I was able to reproduce it in ubuntu precise:

pcmanfm: 0.9.10-0ubuntu2
udisks: 1.0.4-5ubuntu2
policykit-1: 0.104-1

To test it:

1.- Install ubuntu minimal

2.- install pcmanfm and add gvfs support
          $ sudo apt-get install pcmanfm gvfs gvfs-common gvfs-daemons gvfs-fuse gvfs-libs libatasmart4 libdevmapper-event1.02.1 libgdu0 libgnome-keyring-common libgnome-keyring0 libgudev-1.0-0 liblvm2app2.2 libsgutils2-2 udisks

3.- run pcmanfm and you'll notice udisks needs and doesn't have as a dependency policykit-1

          $ sudo apt-get install policykit-1

4.- run again pcmanfm (once policykit-1 is installed) and try to mount an usb, you'll face the "Not authorized" dialog

5- create /etc/polkit-1/localauthority/50-local.d/55-storage.pkla with the following content:

[Storage Permissions]
Identity=unix-group:plugdev
Action=org.freedesktop.udisks.filesystem-mount;org.freedesktop.udisks.drive-eject;org.freedesktop.udisks.drive-detach;org.freedesktop.udisks.luks-unlock;org.freedesktop.udisks.inhibit-polling;org.freedesktop.udisks.drive-set-spindown
ResultAny=yes
ResultActive=yes
ResultInactive=no

6- add yourself to the plugdev group
           $ usermod -a -G plugdev your-username

7- pcmanfm will automount usb disks

Even when exist a workaround, pcmanfm will termine randomly while umounting those disks

--------------------------------------------------
Ubuntu Bug Squad volunteer triager
http://wiki.ubuntu.com/BugSquad