samba - Jul 2002 - NT password server problem (under heavy load)

hi,

i'm using samba on our HP-UX 11.11 server for years without problems.
the samba server is included to a NT domain. the password verification is done 
on the NT PDC (WINNT01) or BDC (WTS01).
since some months our 250 clients update their VIRUS definition files every
2 days at 9 o'clock. (all together at the same time, the clocks are 
sychronised. not really a good idea, i know.)

with samba-2.2.3a there was a message in the log files:
---------------------------------------------------------------------------------------
[2002/05/01 09:00:02, 0] rpc_client/cli_netlogon.c:(157)
  cli_net_auth2: Error NT_STATUS_ACCESS_DENIED
[2002/05/01 09:00:02, 0] rpc_client/cli_login.c:(74)
  cli_nt_setup_creds: auth2 challenge failed
[2002/05/01 09:00:02, 0] smbd/password.c:(1335)
  connect_to_domain_password_server: unable to setup the PDC credentials to 
machine WINNT01. Error was : NT_STATUS_OK.
[2002/05/01 09:00:02, 0] smbd/password.c:(1554)
  domain_client_validate: Domain password server not available.
[2002/05/01 09:00:02, 0] passdb/pdb_smbpasswd.c:(1367)
  unable to open passdb database.
[2002/05/01 09:00:02, 0] passdb/pdb_smbpasswd.c:(1367)
  unable to open passdb database.
[2002/05/03 09:00:07, 0] rpc_client/cli_netlogon.c:(406)
  cli_net_sam_logon_internal: NT_STATUS_ACCESS_DENIED
[2002/05/03 09:00:07, 0] smbd/password.c:(1571)
  domain_client_validate: unable to validate password for user Administrator 
in domain KAPP-NT to Domain controller WINNT01. Error was 
NT_STATUS_ACCESS_DENIED.
----------------------------------------------------------------------------------------
but the whole samba server continues to work.

after i updated to 2.2.4 and 2.2.5 the SAMBA server stops working (no response 
to client PCs) after 9 o'clock for all clients. i see a lot of smbd guest 
connections, and all i see in the log files (loglevel 3) is:
---------------------------------------------------------------------
[2002/07/26 09:00:48, 3] libsmb/namequery.c:(768)
  resolve_lmhosts: Attempting lmhosts lookup for name KAPP-NT<0x1c>
[2002/07/26 09:00:48, 3] libsmb/namequery.c:(709)
  resolve_wins: Attempting wins lookup for name KAPP-NT<0x1c>
[2002/07/26 09:00:48, 3] libsmb/namequery.c:(727)
  resolve_wins: WINS server == <193.97.224.109>
[2002/07/26 09:00:48, 3] lib/util_sock.c:(813)
  bind succeeded on port 0
[2002/07/26 09:00:48, 2] libsmb/namequery.c:(421)
  Got a positive name query response from 193.97.224.109 ( 193.97.224.109 
193.97.224.59 193.97.224.109 )
[2002/07/26 09:00:48, 3] lib/util_sock.c:(813)
  bind succeeded on port 0
[2002/07/26 09:00:48, 3] libsmb/namequery.c:(768)
  resolve_lmhosts: Attempting lmhosts lookup for name WTS01<0x20>
[2002/07/26 09:00:48, 3] libsmb/namequery.c:(808)
  resolve_hosts: Attempting host lookup for name WTS01<0x20>
---------------------------------------------------------------------
i have to stop samba, sometimes kill hanging smbd processes and restart it.
the rest of the day everything runs fine.

is it a SAMBA problem?
why get i password verifycation errors with 2.2.3a 
and only resolver logs before the system hangs with 2.2.5?
or a NT PDC problem? (are the password verification connections limited?)

any ideas?