Comment 33 for bug 1240336

my story:
I use gdm + gnome and upgraded via upgrade manager from 12.10 => 13.04 and also from 13.04 => 13.10.
It worked for some weeks until a week ago. (GDM screen started but no loginwindow)
Switching to terminal (CTRL+ALT+F1) worked.

After a long search I found out that switching from gdm to lightdm brought me back into GUI Mode (sudo dpkg-reconfigure gdm => change to lightdm and reboot)
But then I found out I have permission problems like you described (Softwarecenter install/uninstall, updates, network, USB)

I tried a lot so I can't be sure what the solution was, but the last things I tried were:
#19
* (sudo pam-auth-update --force
* reboot
=> did not work

#23
* add
    session required pam_loginuid.so
    session required pam_systemd.so
  to /etc/pam.d/gdm
* dpkg-reconfigure gdm (and select gdm)
* reboot
=> did not work (still no login window)

#23
* add
    session required pam_loginuid.so
    session required pam_systemd.so
  to /etc/pam.d/lightdm
* dpkg-reconfigure gdm (and select lightdm)
* reboot
=> works! I can change network settings, install/uninstall packages, connect usb devices

#23
* try again "dpkg-reconfigure gdm" (and select gdm)
* (new lines in /etc/pam.d/gdm are already there from previous try)
* reboot
=> works!

I don't know why/how but now also gdm is working again