DO you still have WC Marketplace installed?
At one time you did- because this url is to that plugin’s vendor dashboard: wcmp_vendor_dashboard
http://kidinventor.com/wcmp_vendor_dashboard/
Please be sure the data from that plugin is removed from your site; in addition, make sure your vendor dashboard points to the page that has our shortcode [wcv_vendor_dasbaord] on it, with nothing else. then save your permalinks. (wp admin > settings > permalinks)