WordPress MU

Our site uses wpmu for some content, and it uses wpmu as the authentication for another section of our site.

Our code used to look like this:

require_once("../../subdomains/blogs/httpdocs/wp-config.php");

if (!is_user_logged_in()) auth_redirect();
switch_to_blog(2);

and then it would check the permissions of the user on that blog.

Now, unfortunately requiring the wp-config file seems to redirect us to the main url of the wpmu site. It never even gets to tech if the user is logged in. The subsite is on a different sub domain from wpmu.

Is there some big change that upgrading may have affected?

Thanks,
-Seth