Warning in the plugin. Appointments +

Got this error now.

Warning: Missing argument 2 for Appointments::save_post() in /var/www/clapme.com.br/html/wp-content/plugins/appointments/appointments.php on line 685

Also i'd like to add multiple agendas to use the plugin to create an appointments hub.
And offer to some clients the oportunity to use my site to schedule their users appointments.
I can create that by using a multisite and each client would be a blogMU, but don't know if that's is the right choice.