[Samba] Problems to join domain (clients XP send false SID !)

[kissg]

First of all, try to re-join the machine to your domain. Add the machines to
a local workgroup (you can assign any name to it), then, after a reboot, try
to rejoin the machines to your domain. If this doesn't help, check user data
in the LDAP database:

id <username>

you should see something like this:

uid=10001(administrator) gid=512(Domain Admins) groups=512(Domain
Admins),513(Domain Users)

Check if the gid is:

512 for Domain Administrators
513 for Domain Users
514 for Domain Guests

This is very important, because Windows determines the primary group based
on the group id (for example, if you log in to your domain as the "root"
user, you won't get administrator privileges on the local computer, because
the group ID for root is always zero).