Teu log diz ...

2006/10/16 17:55:26| Squid is already running! Process ID 3937
2006/10/16 18:28:30| ACL name 'permitidos' not defined!
FATAL: Bungled squid.conf line 123: http_access allow permitidos
Squid Cache (Version 2.5.STABLE6): Terminated abnormally.
2006/10/16 18:28:30| ACL name 'permitidos' not defined!
FATAL: Bungled squid.conf line 123: http_access allow permitidos
Squid Cache (Version 2.5.STABLE6): Terminated abnormally.
2006/10/16 18:35:25| ACL name 'permitidos' not defined!
FATAL: Bungled squid.conf line 123: http_access allow permitidos
Squid Cache (Version 2.5.STABLE6): Terminated abnormally.
2006/10/16 18:35:25| ACL name 'permitidos' not defined!
FATAL: Bungled squid.conf line 123: http_access allow permitidos
Squid Cache (Version 2.5.STABLE6): Terminated abnormally.
2006/10/17 08:25:38| Squid is already running! Process ID 6031

Você não especificou a ACL name 'permitidos' not defined!
não tem a ver com o problema da autenticação ... mais é um erro que vi no seu log ...

Falow ..