samba version:3.4.2
platform OS: linux-2.6.21

i share a directory "netdisk" to windows through samba, i want to share this directory to guest, we need the guest only have read permission to this directory and have rwx permission to its subdirectories. so i set "guest account" = a non-root user i created in linux, but i can't start smbd "/usr/bin/smbd -D" , but if i use "guest account = root" smbd work well, here is the error log:
 " 
[1970/01/01 01:09:27,  0] lib/util.c:1480(smb_panic)
  PANIC (pid 797): failed to set gid

[1970/01/01 01:09:27,  0] lib/util.c:1584(log_stack_trace)
  BACKTRACE: 1 stack frames:
   #0 /usr/bin/smbd(log_stack_trace+0x38) [0x6d89d8]
[1970/01/01 01:09:27,  0] lib/fault.c:307(dump_core)
  Can not dump core: corepath not set up

" 


and my smb.conf is:

==============================================================\

[global]
workgroup = eapac
use mmap = no
log level = 1
max log size = 2000
log file = /tmp/samba.log
guest account = zzz  （a user ,gid = 500, uid =500）
dos charset = UTF-8
unix charset = UTF-8
display charset = UTF-8
socket options = SO_KEEPALIVE TCP_NODELAY IPTOS_LOWDELAY

netbios name = t083gTest
server string = test
oplocks = false
dns proxy = no
#security = user
security = share
encrypt passwords = yes
#smb passwd file = /var/run/samba/smbpasswd
disable spoolss = yes
hosts allow = All
interfaces = bridge0

[netdisk]
comment = usb disk
path = /netdisk
read only = no
writeable = yes
guest ok = yes
======================================================================


thanks