[John James Jacoby]

Arturo, in order to make it work correctly with current versions of BP/WP/WPMU you might need to add an undocumented variable to your wp-config.php file. Some people have needed to, others have not.

define('WP_AUTH_COOKIE_VERSION', 1);

This isn’t a magic fix, but if you’ve tried EVERYTHING and are banging your head against a cookie wall, try this.