can't become user

[Francesc Guasch]

Hi. I have installed samba before. This time I cannot even do
a smbclient -L localhost. When I try to connect I get
that log:

[1999/03/15 11:37:32, 0] smbd/uid.c:become_gid(105)
  Couldn't set effective gid to 408 currently set to (real=0,eff=0)
[1999/03/15 11:37:32, 0] smbd/service.c:make_connection(425)
  Can't become connected user!
[1999/03/15 11:37:50, 0] smbd/uid.c:become_gid(105)
  Couldn't set effective gid to 0 currently set to (real=0,eff=0)
[1999/03/15 11:37:50, 0] smbd/service.c:make_connection(425)
  Can't become connected user!

I searched the archives unsuccessfully. What am I missing ?
thank you.