I have a freshly setup 12.04 LTS pc system (120 GB SSD, 1 TB HDD, 16 GiB RAM); since a few days, I can't login to the graphical desktop anymore: there is very short flashing shell window which disappears very quickly, and I'm confronted with the login screen again. I believe there is something about modprobe and vbox, but I can't read it fast enough ...

I can login to a terminal (Ctrl+Alt+F1). It did not help to chown all contents of my home directory to me:my-group, like suggested here.

This is what I could find in /var/log, grepping for the date and time (I inserted linebreaks after <my-hostname>; real time values preserved):

auth.log:

<date> 22:43:01 <my-hostname>
    lightdm: pam_succeed_if(lightdm:auth): requirement "user ingroup nopasswdlogin" not met by user "tobias"
<date> 22:43:08 <my-hostname>
    lightdm: pam_unix(lightdm:session): session closed for user lightdm
<date> 22:43:08 <my-hostname>
    lightdm: pam_unix(lightdm:session): session opened for user tobias by (uid=0)
<date> 22:43:08 <my-hostname>
    lightdm: pam_ck_connector(lightdm:session): nox11 mode, ignoring PAM_TTY :0
<date> 22:43:08 <my-hostname>
    lightdm: pam_unix(lightdm:session): session closed for user tobias
<date> 22:43:09 <my-hostname>
    lightdm: pam_unix(lightdm:session): session opened for user lightdm by (uid=0)
<date> 22:43:09 <my-hostname>
    lightdm: pam_ck_connector(lightdm:session): nox11 mode, ignoring PAM_TTY :0
<date> 22:43:10 <my-hostname>
    lightdm: pam_succeed_if(lightdm:auth): requirement "user ingroup nopasswdlogin" not met by user "tobias"
<date> 22:43:10 <my-hostname>
    dbus[756]: [system] Rejected send message, 2 matched rules; type="method_call", sender="1:43" (uid=104 pid=1639 comm="/usr/lib/indicator-datetime/indicator-datetime-ser") interface="org.freedesktop.DBus.Properties" member="GetAll" error name="(unset)" requested_reply="0" destination=":1.15" (uid=0 pid=1005 comm="/usr/sbin/console-kit-daemon --no-daemon ")

kern.log:

<date> 22:43:00 <my-hostname>
    kernel: [   16.084525] eth0: no IPv6 routers present

syslog:

<date> 22:43:00 <my-hostname>
    kernel: [   16.084525] eth0: no IPv6 routers present
<date> 22:43:01 <my-hostname>
    ntpdate[1492]: adjust time server 91.189.94.4 offset -0.162831 sec
<date> 22:43:08 <my-hostname>
    acpid: client 969[0:0] has disconnected
<date> 22:43:08 <my-hostname>
    acpid: client connected from 1553[0:0]
<date> 22:43:08 <my-hostname>
    acpid: 1 client rule loaded

I have Virtualbox and Truecrypt installed, but I can't think of a reason why they might prevent a graphical login.

I'm confused:

• What is this about requirement "user ingroup nopasswdlogin" not met? I do login using a password, and the password works ok when logging in to a terminal!
• Can I somehow read the error output, e.g. by delaying it, redirecting it to a file, or having the system prompt me for pressing a key?
• Has possibly any recent update caused my problem? Should I install the pending updates? How, btw, without access to the graphical UI?

I have some working knowledge about the Linux shell, but I'm new to Ubuntu. Any help would be appreciated.