I run Debian testing on my laptop. It was OK until I ran aptitude update and then aptitude upgrade, and then a reboot.

Now, the system boots into the normal gnome login screen. I login as my normal user, the background comes up, the disk light flashes as expected, then I get an error message on a black screen -

Oh no, something has gone wrong!
A problem has occurred, and the system cannot recover. All extensions have been disabled as a precaution.

Then, a dialog pops up with an OK button, which says:
No system tray detected on this system.
Unable to start, exiting.

I click OK, the system reverts back to the login screen.

I can access a shell prompt with ctrl-f2. Dmesg does not show any errors. I tried adding a new user, rebooting, and logging in as the new user, but I get the same error messages.

Googling the errors "debian missing system tray" did not yield much in the way of help. Googling "Oh no..." led me to looking at the errors from startx. I ran startx from the command line and wrote the errors to a file. I got the following:

X.Org X Server 1.12.4
Release Date: 2012-08-27
X Protocol Version 11, Revision 0
Build Operating System: Linux 3.2.0-4-amd64 x86_64 Debian
Current Operating System: Linux orca 3.1.0-1-amd64 #1 SMP Tue Jan 10 05:01:58 UTC 2012 x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.1.0-1-amd64 root=UUID=7870a6c9-642b-4b15-b0cd-3f01d27
d450e ro quiet
Build Date: 17 April 2013  10:22:47AM
xorg-server 2:1.12.4-6 (Julien Cristau <jcristau@debian.org>)
Current version of pixman: 0.26.0
        Before reporting problems, check http://wiki.x.org
        to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
        (++) from command line, (!!) notice, (II) informational,
        (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.1.log", Time: Sun Jun 30 17:34:20 2013
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
libkmod: ERROR ../libkmod/libkmod.c:505 kmod_lookup_alias_from_builtin_file: could not open builtin f
ile '/lib/modules/3.1.0-1-amd64/modules.builtin.bin'
FATAL: Module fbcon not found.
The XKEYBOARD keymap compiler (xkbcomp) reports:
> Warning:          Compat map for group 2 redefined
>                   Using new definition
> Warning:          Compat map for group 3 redefined
>                   Using new definition
> Warning:          Compat map for group 4 redefined
>                   Using new definition
Errors from xkbcomp are not fatal to the X server
The XKEYBOARD keymap compiler (xkbcomp) reports:
> Warning:          Compat map for group 2 redefined
>                   Using new definition
> Warning:          Compat map for group 3 redefined
>                   Using new definition
> Warning:          Compat map for group 4 redefined
>                   Using new definition
Errors from xkbcomp are not fatal to the X server
xinit: connection to X server lost

waiting for X server to shut down Server terminated successfully (0). Closing log file.

It seems the fbcon error is a red herring....fbcon was moved into the kernel and the error message has not been fixed: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=588560

My /lib/modules/3.1.0-1-amd64/modules.builtin.bin has zero length. According to this bug report (http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=668568) the modules.builtin.bin is not used until 3.2.1-1, so I am lost at this point.

Any suggestions on how to diagnose/fix this problem would be greatly appreciated!

Mark