Redirect loop with fresh subdirectory multisite install

Hi, I just set up a fresh multisite install at http://www.example.com. The frontend is working fine, as is the Dashboard for the first site (which is just at http://www.example.com). However, when I created my first network site, while the front end works (www.example.com/first), trying to visit the dashboard (www.example.com/first/wp-admin) gives me a redirect loop error.

I've looked at many of the existing threads, both here and elsewhere, but haven't come up with anything.

I've tried various .htaccess files, the one that comes up most recently is attached. Here's the relevant portion of my wp-config.php:

define('WP_HOME','www.example.com');
define('WP_SITEURL',WP_HOME);

/* Multisite */
define('MULTISITE', true);
define('SUBDOMAIN_INSTALL', false);
define('DOMAIN_CURRENT_SITE', WP_HOME);
define('PATH_CURRENT_SITE', '/');
define('SITE_ID_CURRENT_SITE', 1);
define('BLOG_ID_CURRENT_SITE', 1);

Any help would be appreciated. Thanks!