Evidentemente
http://192.168.1.2:8085/sgerror.php?url=blank&msg=http%3A%2F%2Fwww.dsvalpo.cl%2Ferror%2Ferrorsquid3.html&a=%a&n=%n&i=%i&s=%s&t=%t&u=%u
no es
www.dsvalpo.cl/error/errorsquid3.html
Edita ese campo en la configuración de squidGuard vía interfase web, a ver si te genera lo que tú quieres o no.
Redirect mode –-> ext url redirect (enter URL)
Redirect info -----> www.dsvalpo.cl/error/errorsquid3.html
No tienes caracteres raros. Son parámetros que se pueden pasar a la página de error:
http://www.squidguard.org/Doc/redirect.html
%a Variable that holds the IP address of the client.
%i Variable that holds the user ID (RFC931, LDAP or mySQL) or "unknown" if not available.
%n Variable that holds the domainname of the client or "unknown" if not available.
%p Variable that holds the REQUEST_URI, i.e. the path and the optional query string of %u, but note for convenience without the leading "/".
%s Variable that holds the matched source group (client group) or "unknown" if no groups were matched.
%t Variable that holds the matched destination group (target group) or "unknown" if no groups were matched.
%u Variable that holds the requested URL.
Que estén o no esos valores dependen de cómo sea la instalación.