[Samba] If I use "valid users" option, I can't log into the domain

[Steve A]

Samba 3.0.22-1 on FC5

I can log into the domain, but if I set the "valid users" option to 
"@users", I can't log in anymore to my Samba domain.

My user is a member of Unix group "users"
Unix group "users" is mapped to Windows group "Domain Users"
I can still access \\<samba_server>

... but I can't log into the Samba domain.

Where am I going wrong?


Thanks,
Steve :)