samba - Sep 2007 - Unable to find the Domain Master Browser

I have samba with this global

[global]
        workgroup = DEPANIZZA
        interfaces = eth1
        bind interfaces only = Yes
        obey pam restrictions = Yes
        passdb backend = tdbsam
        passwd program = /usr/bin/passwd %u
        passwd chat = *Enter\snew\sUNIX\spassword:* %n\n 
*Retype\snew\sUNIX\spassword:* %n\n *password\supdated\ssuccessfully* .
        syslog = 0
        log file = /var/log/samba/log.%m
        max log size = 1000
        name resolve order = lmhosts  wins host bcast
        dns proxy = No
        wins support = Yes
        panic action = /usr/share/samba/panic-action %d
        invalid users = root
from some days it is not possible to open the workgroup list from 
Windows pcs.

The error in nmd.log is

[2007/09/21 18:01:35, 0] 
nmbd/nmbd_browsesync.c:find_domain_master_name_query_fail(351)
  find_domain_master_name_query_fail:
  Unable to find the Domain Master Browser name DEPANIZZA<1b> for the 
workgroup DEPANIZZA.
  Unable to sync browse lists in this workgroup.

thanks

-- 
ing. Paolo Mastromarco
tel. +39.3482560898
p.mastromarco@depanizzaimp.it