Flush Rewrite Rules when new site is created on network
You need to create a hook for wpmu_new_blog action: add_action( ‘wpmu_new_blog’, ‘wpse8170_wpmu_new_blog’ ); function wpse8170_wpmu_new_blog( $blog_id ) { switch_to_blog( $blog_id ); flush_rewrite_rules(); restore_current_blog(); }