BuddyPress.org

@romik84 – I saw your post on here:
https://wordpress.org/support/topic/415399

I haven’t looked too far into this, but there doesn’t appear to be a “wpmu_new_blog” filter:
add_filter('wpmu_new_blog', array(&$cets_wpmubt, 'set_new_blog_topic'), 101);

However, there is an action called “wpmu_new_blog”, maybe that is what the plugin author meant?
add_action('wpmu_new_blog', array(&$cets_wpmubt, 'set_new_blog_topic'), 101);