Comment 28 for bug 291467

i do not know if that error is really of significance...
i have this, too:

gnome-session[15895]: WARNING: Application 'gnome-wm.desktop' failed to register before timeout

i discovered that compiz was making gconf2 angry, pushing cpu up to constant 20% after login and making machine slow.

after all the following did the trick:

i wrote a delay-script for starting up compiz. delayed for 10sec.
since than gconf2 is quiet, behaving nomal.

1)
system>preferences>appearance>visual effects> set to "none"

2)
open terminal and do:

$ sudo gedit /home/where/ever/compizdelay.sh

paste this text and save:

#!/bin/bash
  sleep 10
  compiz --loose-binding --replace &
  emerald --replace &
exit 0

3)
now we need to make it executable:
$ sudo chmod +x /home/where/ever/compizdelay.sh

4)
and then under
system>preferences>sessions> press "add" and browse to where that new script is.

test and reboot and voila, works,,,
if not try to play with the "sleep ..." setting in the script, perhaps on your maschine it needs to sleep longer