[Samba] squid + external_acl_type + wbinfo_group.pl, Help needed

[updatemyself .]

Hi All,

i was trying to configure proxy server, which will authenticate only
for the users in group called  "internet" that's in my Windows2003 ADS
previously i configured my proxy server for all users in my domain
and it was working well
i think, i have some problem using external_acl_typel

Please Help

Following is my present squid configuration
squid-2.5.STABLE6-3.4E.11
=========================================================
auth_param ntlm program /usr/bin/ntlm_auth --helper-protocol=squid-2.5-ntlmssp
auth_param ntlm children 30
auth_param ntlm max_challenge_reuses 0
auth_param ntlm max_challenge_lifetime 2 minutes

external_acl_type nt_group ttl=0 concurrency=5 %LOGIN
/usr/lib/squid/wbinfo_group.pl

acl unrestrictedusers external nt_group internet
http_access allow unrestrictedusers
==========================================================
samba-3.0.21c-1

[global]

   workgroup = DNA
   server string = Samba Server
   log level = 3
   log file = /var/log/samba/samba.log
   max log size = 1024
   security = ads
   encrypt passwords = yes
   socket options = TCP_NODELAY SO_RCVBUF=8192 SO_SNDBUF=8192
   dns proxy = no

#=============== Share Definitions ===================#

   password server = 172.16.20.200
   realm = DNA.COM
   idmap uid = 16777216-33554431
   idmap gid = 16777216-33554431
   template shell = /bin/bash
   template homedir = /home/%D/%U
   allow trusted domains = no
   idmap backend = idmap_rid:DNA=16777216-33554431
   winbind use default domain = yes

=====================================================
Operating System
Red Hat Enterprise Linux ES (2.6.9-22.ELsmp)

with this configuration its asking for authentication, but even if we
provide correct username and password its not authenticating

Thank You In Advance
jerrynikky.