samba - Mar 2004 - Samba 3.0.2a + Win2K clients: unreliable share access

After upgrading from 3.0.1 to 3.0.2a, accessing a shared folder has become
unreliable: after being able to access my shares for some time I get an error
message "No domain contoller was available" (actually, I'm
paraphrasing that one, I unfortunately did not record it verbatim).  Host linux
log contains the following error message for each access:

Mar  5 20:07:08 sharesmb01 smbd[4691]: [2004/03/05 20:07:08, 0]
auth/auth_winbind.c: check_winbind_security(122)
Mar  5 20:07:08 sharesmb01 smbd[4691]:   check_winbind_security: ERROR! 
my_private_data == NULL!

Googling the error message just led me to the source file for auth_winbind.c  

Any ideas for where I might try to find more info troubleshooting this?
>From smb.conf (machine, domain and user names altered):
# Global parameters
[global]
	workgroup = domain01
	server string = sharesmb01 (Samba server)
	security = DOMAIN
	passwd program = /usr/bin/passwd %u
	passwd chat = *New*password* %n\n *Retype*new*password* %n\n
*passwd:*all*authentication*tokens*updated*successfully*
	client lanman auth = No
	client plaintext auth = No
	log file = /var/log/samba/%m.log
	max log size = 0
	min protocol = NT1
	socket options = TCP_NODELAY IPTOS_THROUGHPUT SO_SNDBUF=32768 SO_RCVBUF=32768
	dns proxy = No
	wins server = 172.16.10.16
	ldap ssl = no
	idmap uid = 10000-20000
	idmap gid = 10000-20000
	template homedir = /mnt/k/users/%U
	template shell = /bin/bash
	winbind use default domain = Yes
	printing = cups

[printers]
	comment = All Printers
	path = /var/spool/samba
	printable = Yes
	browseable = No

[SASFiles]
	comment = SMB-shared SAS files
	path = /home/SASFiles
	invalid users = +nobody
	force user = SomeUser
	force group = +Domain Users
	read only = No
	create mask = 0777
	directory mask = 0777
	hosts allow = 127., 172.16.10.