After the updates from today (~100) lxdm doesn't start anymore. I tried to use gdm but the same problem happens. /var/log/Xorg.0.log says:

[   605.117] [dix] Could not init font path element built-ins, removing from list!
[   605.117] 
Fatal server error:
[   605.117] could not open default font 'fixed'
[   605.117] 
Please consult the The X.Org Foundation support 
 for help. 
[   605.117] Please also check the log file at "/var/log/Xorg.0.log" for additional information.
[   605.117] 
[   605.850]  ddxSigGiveUp: Closing log
[   605.850] Server terminated with error (1). Closing log file.
I have now downgraded to 12.04 and all is working fine. Has somebody an idea which package triggered this problem?