Site looping when ldap sso refused: Trying to get property of non-object in drupal_lookup_path() (line 77 of /var/www/includes/p

I've a hook that refuses access for certain users to login ( LdapAuthenticationConf.class.php, allowuser(), see #1634930). When it refuses access, a watchdog message appears:
"Trying to get property of non-object in drupal_lookup_path() (line 77 of /var/www/includes/path.inc"

And the site goes into a loop, it tries to authenticate many times, and each time it adds on to the language prefix (to a multi lang using lang prefixes) site. The URL becomes
http://mysite/user/login/sso?destination=en/en/en/en/en/en/en/en/en/en
Which in turn leads too:
Error 310 (net::ERR_TOO_MANY_REDIRECTS)

The sso module is enabled, and in this test case the user is already logged in via kerberos (to windows/AD). So the browser has an identify, and will probably try to authenticate several times.

The code in path.inc is:
// If no language is explicitly specified we default to the current URL
// language. If we used a language different from the one conveyed by the
// requested URL, we might end up being unable to check if there is a path
// alias matching the URL path.
$path_language = $path_language ? $path_language : $language_url->language;

So it looks like the language context is being lost.

Questions:
- How can one stop the sso from constantly authenticating?
- Any tips of how to keep the language content, so that core stops adding on the prefix