I have same problem after upgrade from jaunty to karmic. It seems that there is no default values in gconf, it is not registered gconf schema for gnome-session.
Try
martin@bedna:~$ sudo gconf-schemas --register gnome-session.schemas
This works for me.
I have same problem after upgrade from jaunty to karmic. It seems that there is no default values in gconf, it is not registered gconf schema for gnome-session. schemas
Try
martin@bedna:~$ sudo gconf-schemas --register gnome-session.
This works for me.