I get the same error on my site (WordPress 3.6):
Warning: Missing argument 2 for wpdb::prepare(), called in /usr/home/web/users/xxxxxxx/html/lc/wp-content/plugins/rsvp/rsvp_frontend.inc.php on line 712 and defined in /usr/home/web/users/xxxxxxx/html/lc/wp-includes/wp-db.php on line 992
Any fix?
