Supported Samba Releases
Squid 2.5 uses an internal Samba interface to communicate with the winbindd daemon. It is therefore sensitive to any changes the Samba team may make to the interface.

The winbind helpers shipped with Squid-2.5.STABLE2 supports Samba-2.2.6 to Samba-2.2.7a and hopefully later Samba-2.X versions. To use Squid-2.5.STABLE2 with Samba versions 2.2.5 or ealier the new --with-samba-sources=... configure option is required. This may also be the case with Samba-2.2.X versions later than 2.2.7a or if you have applied any winbind related patches to your Samba tree.

Squid-2.5.STABLE1 supported Samba 2.2.4 or 2.2.5 only. Use of Squid-2.5.STABLE2 or later recommended with current Samba-2.X releases.

For Samba-3.X the winbind helpers shipped with Squid should not be used (and won't work if your attempt to do so), instead the ntlm_auth helper shipped as part of the Samba-3 distribution should be used. This helper supports all versions of Squid and both the ntlm and basic authentication schemes. For details on how to use this Samba helper see the Samba documentation. For group membership lookups the wbinfo_group helper shipped with Squid can be used (this is just a wrapper around the samba wbinfo program and works with all versions of Samba)

http://www.squid-cache.org/Doc/FAQ/FAQ-23.html