samba - Dec 2003 - primary gid of user [root] is not a Domain group

I have found this on log.smbd. What does it mean? How can I fix this?

  rpc_server/srv_util.c:get_domain_user_groups(371)
  get_domain_user_groups: primary gid of user [root] is not a Domain group !
  get_domain_user_groups: You should fix it, NT doesn't like that