You get the following message in your squid’s cache.log:

[2010/03/19 07:04:23, 0] utils/ntlm_auth.c:winbind_pw_check(545)

Login for user [DOMAIN]\[USER]@[COMPUTER] failed due to [winbind client not authorized to use winbindd_pam_auth_crap. Ensure permissions on /var/run/samba/winbindd_privileged are set correctly. ]

Solution: Ensure that the permissions are set to the following:

drwxr-x— root winbindd_priv

You can set them by invoking: chmod 750 /var/run/samba/winbindd_privileged

Check your /etc/group and add the proxy user to the winbindd_priv group.