Consolekit session not active

Binary package hint: upstart

Ubuntu Lucid Lynx, i386, all updates installed, starting from a fresh install.

The system seems to boot normally, but the splash screen is not shown and there is no drum sound in gdm.
When switching to the console, there is __no__ login screen.
Logging in using gdm, there is no login sound either and usb sticks can't be mounted, as the user is "not authorized".
The reason for the behaviour after login seems to be console-kit:

$ ck-list-sessions
Session2:
 unix-user = '1000'
 realname = '****'
 seat = 'Seat1'
 session-type = ''
 active = FALSE
 x11-display = ':0'
 x11-display-device = '/dev/tty7'
 display-device = ''
 remote-host-name = ''
 is-local = TRUE
 on-since = '2010-05-24T08:20:08.353095Z'
 login-session-id = ''

The session is not active!

I found it curious, that there was no terminal login prompt, so I tried to figure out, how to debug upstart. Therefore I inserted the option "--debug" into grub.conf (for the record: via /etc/default/grub) et voilà: the system boots up normally (except for all the debug messages).

I assume, that the problem occurred via update, as I updated the system yesterday, after installing it and the problem occurred this morning. It seems to be somehow tied to this machine, which isn't mine. As before yesterday's reinstall, there was also a fresh install of 10.4 on this machine and it had in retrospect the same problem.

Description: Ubuntu 10.04 LTS
Release: 10.04