[Plugin: RSVPmaker] error when choosing rsvp

I am getting :

Catchable fatal error: Object of class WP_Error could not be converted to string in /home/mmwealth/mmwealth.com/wp-content/themes/simplybiz/library/includes/breadcrumb.php on line 15
Is this a known bug?

http://ww.wp.xz.cn/extend/plugins/rsvpmaker/