i got core-dump when trying to start winbind (after joining w2k domain). i don't think (correct me if wrong) that smb.conf or the lab setup is relevant in this case because the stack-trace explains exactly what caused the abort. regardless of the lab setup, still winbind should defend itself from signal-11. the problem i see is in cli_close call but here's the trace:

[2006/07/10 07:45:00, 0] lib/util_sock.c:read_socket_with_timeout(489)
  read_socket_with_timeout: timeout read. read error = Connection reset by peer.
[2006/07/10 07:45:00, 0] rpc_client/cli_pipe.c:rpc_api_pipe(437)
  cli_pipe: return critical error. Error was Read error: Connection reset by peer
[2006/07/10 07:45:00, 0] rpc_client/cli_pipe.c:cli_rpc_close(1763)
  cli_rpc_open failed on pipe \samr to machine LAB-DC-MAIN.  Error was Read error: Connection reset by peer
[2006/07/10 07:45:00, 0] rpc_client/cli_pipe.c:cli_rpc_close(1763)
  cli_rpc_open failed on pipe \lsarpc to machine LAB-DC-MAIN.  Error was Read error: Connection reset by peer
[2006/07/10 07:46:00, 1] nsswitch/winbindd_cm.c:cm_prepare_connection(255)
  cli_negprot failed
[2006/07/10 07:46:26, 1] nsswitch/winbindd_cm.c:cm_prepare_connection(255)
  cli_negprot failed
[2006/07/10 07:47:23, 0] lib/fault.c:fault_report(36)
  ===============================================================
[2006/07/10 07:47:23, 0] lib/fault.c:fault_report(37)
  INTERNAL ERROR: Signal 11 in pid 3821 (3.0.20)
  Please read the appendix Bugs of the Samba HOWTO collection
[2006/07/10 07:47:23, 0] lib/fault.c:fault_report(39)
  ===============================================================
[2006/07/10 07:47:23, 0] lib/util.c:smb_panic2(1548)
  PANIC: internal error
[2006/07/10 07:47:23, 0] lib/util.c:smb_panic2(1555)
  BACKTRACE: 29 stack frames:
   #0 /usr/sbin/winbindd(smb_panic2+0x1d6) [0x80e6436]
   #1 /usr/sbin/winbindd(smb_panic+0x13) [0x80e6253]
   #2 /usr/sbin/winbindd [0x80cf307]
   #3 /usr/sbin/winbindd [0x80cf381]
   #4 /lib/libc.so.6 [0x25a3cd18]
   #5 /usr/sbin/winbindd(cli_close+0x1b) [0x810cedb]
   #6 /usr/sbin/winbindd(cli_nt_session_close+0xcd) [0x810637d]
   #7 /usr/sbin/winbindd(cli_close_connection+0x11) [0x8106421]
   #8 /usr/sbin/winbindd(cli_shutdown+0x1d) [0x81065cd]
   #9 /usr/sbin/winbindd(invalidate_cm_connection+0xab) [0x80895cb]
   #10 /usr/sbin/winbindd [0x8089814]
   #11 /usr/sbin/winbindd(cm_connect_lsa+0x16) [0x8089e56]
   #12 /usr/sbin/winbindd(msrpc_name_to_sid+0x200) [0x808b840]
   #13 /usr/sbin/winbindd [0x808d2b5]
   #14 /usr/sbin/winbindd [0x807f7c7]
   #15 /usr/sbin/winbindd(winbindd_lookup_sid_by_name+0x2d) [0x807b5ad]
   #16 /usr/sbin/winbindd(winbindd_dual_lookupname+0xf2) [0x8093dd2]
   #17 /usr/sbin/winbindd [0x8091b1a]
   #18 /usr/sbin/winbindd [0x80920a1]
   #19 /usr/sbin/winbindd [0x8091704]
   #20 /usr/sbin/winbindd(async_request+0x1a5) [0x8091405]
   #21 /usr/sbin/winbindd(init_child_connection+0x21d) [0x807aabd]
   #22 /usr/sbin/winbindd(async_domain_request+0x109) [0x8091879]
   #23 /usr/sbin/winbindd [0x807a4c3]
   #24 /usr/sbin/winbindd(rescan_trusted_domains+0x47) [0x807a887]
   #25 /usr/sbin/winbindd [0x8073bb4]
   #26 /usr/sbin/winbindd(main+0x5a5) [0x8074825]
   #27 /lib/libc.so.6(__libc_start_main+0x8e) [0x25a2a3b6]
   #28 /usr/sbin/winbindd(chroot+0x39) [0x8072601]
[2006/07/10 09:57:06, 0] rpc_client/cli_pipe.c:rpc_api_pipe(437)
  cli_pipe: return critical error. Error was Call timed out: server did not respond after 10000 milliseconds
[2006/07/10 09:57:06, 0] rpc_client/cli_pipe.c:cli_rpc_close(1763)
  cli_rpc_open failed on pipe \NETLOGON to machine LAB-DC-MAIN.  Error was Call timed out: server did not respond after 10000 milliseconds
[2006/07/10 09:57:06, 0] rpc_client/cli_pipe.c:cli_rpc_close(1763)
  cli_rpc_open failed on pipe \NETLOGON to machine LAB-DC-MAIN.  Error was Call timed out: server did not respond after 10000 milliseconds
[2006/07/10 13:15:00, 0] lib/util_sock.c:read_socket_with_timeout(489)
  read_socket_with_timeout: timeout read. read error = Connection reset by peer.
[2006/07/10 13:15:00, 0] rpc_client/cli_pipe.c:rpc_api_pipe(437)
  cli_pipe: return critical error. Error was Read error: Connection reset by peer
[2006/07/10 13:15:00, 0] rpc_client/cli_pipe.c:cli_rpc_close(1763)
  cli_rpc_open failed on pipe \samr to machine LAB-DC-MAIN.  Error was Read error: Connection reset by peer
[2006/07/10 13:15:00, 0] rpc_client/cli_pipe.c:cli_rpc_close(1763)
  cli_rpc_open failed on pipe \lsarpc to machine LAB-DC-MAIN.  Error was Read error: Connection reset by peer
[2006/07/10 13:15:00, 0] rpc_client/cli_pipe.c:cli_rpc_close(1763)
  cli_rpc_open failed on pipe \NETLOGON to machine LAB-DC-MAIN.  Error was Read error: Connection reset by peer
[2006/07/10 13:15:00, 0] rpc_client/cli_pipe.c:cli_rpc_close(1763)
  cli_rpc_open failed on pipe \NETLOGON to machine LAB-DC-MAIN.  Error was Read error: Connection reset by peer