samba - Nov 2006 - 3.0.22-3.0.23 upgrade -> problems with session closing unexpectly

Short problem description:
I can login (XP Home) to samba server and open files. After quite short
period of time, connection closes unexpectly and login window appears.
I can login again and same story repeats.
There is nothing unusual in logs besides:

    smbldap_open: cannot access LDAP when not root..

Samba works as stand-alone server, with LDAP user database.

Any ideas?