gdm and radius accounting

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Hello everybody,
I simply and correctly setup my ubuntu linux box to use freeradius
authentication; actually the problem is that I'm not able to use
radius accounting.
I think that I correctly setup my radius server to use sql as
accounting mode but the radius server neither receives accounting
packets from the client (I see it starting the server with the -XXX
option).
The only "accounting" thing that it's saving in the sql db is the post
auth section that inserts a line for a correct authentication
response.

on the client side I only modified the pam - gdm configuration file that is

#%PAM-1.0
auth    requisite       pam_nologin.so
auth    sufficient      pam_radius_auth.so
auth    required        pam_env.so readenv=1
auth    required        pam_env.so readenv=1 envfile=/etc/default/locale
@include common-auth
auth    optional        pam_gnome_keyring.so
account	required	pam_radius_auth.so
@include common-account
session required        pam_limits.so
@include common-session
session optional        pam_gnome_keyring.so  auto_start
@include common-password

whitch step have I forgotten? what's wrong?

thank you for your help,
sub