[Samba] problems with username map

[HeRnAn DeL bOcA]

if someone knows anything about this problem???

with samba 2.2.7  i've used a username map called smbusers file with this structure

user_domain ="user at domain"
user2_domain = "user2 at domain"
and so on.
obviosuly in the smb.conf the option is enable username map = /etc/samba/smbusers
and it worked just fine

but now i upgraded samba to 3.0 and the option "username map" is not working.... is there any solution??? 

thanks to anybody that can help me

Hernan