[Samba] xbox accessing samba shares

[ianux]

I've got a network running XP, 98SE, a Xbox and linux running Samba 2.2.8a
(most of the time all together).
in the windows neighbourhood, everything is fine, every one see each other
and right shares.
Here is my problem : I'm running XBMP on the Xbox, which is capable to
access SBM shares to play video and music. But when I'm watching a video
located on my linux box, the streaming stops (and the console crashes)
after exactly 8 minutes. It's only the case with my linux box.
My important samba settings are, IMO :
security = share
encrypt passwords = yes
socket options = TCP_NODELAY SO_RCVBUF=8192 SO_SNDBUF=8192
and no passwd file (the line
smb passwd file = /etc/samba/private/smbpasswd
is commented)
the log produces regularly this line (with loglevel 3):
nmbd/nmbd_responserecordsdb.c:find_response_record(235)
find_response_record: response packet id 23310 received with no matching record.
what is the problem ?