i can not use gnome/openbox

[waterloo]

I install openbox in gentoo with gnome .
now I can use openbox lonely from gdm .
when I use  gnome 2.22 ,I can use gnome/openbox.
after I update to gnome 2.24, I can not use gnome/openbox .

it displays:
your session only lasted less than 10 seconds. if you have not logged out
yourself , this could mean that there is some installation problem or that
you may be out of diskspace . Try logging in with one of the failsafe
sessions to see if you can fix this problem.

below is my ~/.xsession-errors file
/etc/X11/gdm/Xsession: Beginning session setup...
non-network local connections being added to access control list
/etc/X11/gdm/Xsession: Setup done, will execute: /usr/bin/ssh-agent --
/usr/bin/seahorse-agent --execute /usr/bin/openbox-gnome-session
gnome session warning unknown option --choose-session=openbox-session

how to fix it ? thanks
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