From the Samba FAQ:
http://us1.samba.org/samba/docs/FAQ/#4> Unknown parameter encountered: "domain controller"
> Ignoring unknown parameter "domain controller"
As of 1.9.18 the "domain controller" parameter has changed. You should
not need it, but in it's place may need "networkstation user logon = yes".
Please check the smb.conf man page BEFORE using this option so you
understand it's significance.