samba - Nov 2003 - Spnego =no,xp , security = domain ask for more info

I've got a samba server with security = domain. 
With win98 I can connect to this server without any problem. The pdc
auth the user.
With xp client I must set spnego=no in the smb.conf of the server (
without that only security = server works )
My xp client and user  can auth directly on the samba DC  without any
kind of problems.

Can someone explain me  ?

Jean-marc