Comment 4 for bug 285937

This is related to the move of gconf from corba to DBus.

Because gconf is now over the session dbus, you can't talk to it from cron.

There's a way around this, which is to locate one process running in your dbus session and reading the "DBUS_SESSION_BUS_ADDRESS" env var from it; for instance:
xargs -n 1 -0 echo </proc/$(pidof x-session-manager)/environ | grep -Z DBUS_SESSION_BUS_ADDRESS=