samba - Apr 1998 - problems with security=user

Hello,

I am running Samba 1.9.18p4 on Linux Redhat 5.0. Clients are Windows 
95 SR2 and Windows NT 4.0 SP1.

Clients that do not have a Linux account
- can't browse Samba's services
- can't access public shares

With security=share it works.
I have guest account correctly set.

What can be wrong?

Thanks.
Frantisek Bocek