admin-ajax.php return error 500

Hi, i have a problem in my multisite installation :
The url request for admin-ajax.php return a error 500 :
https://mainsite/subsite/wp-admin/admin-ajax.php?action=WP_FullCalendar&type=patient&post__in=708&post_type=patient&posts_per_page=-1&month=0&year=2016&start=2015-12-28&end=2016-02-08&_=1453829882873

I have tried this :
WP Fullcalendar network activated
WP Fullcalendar subsite activated
And also trying to disable Domain Maping extension option :
“Redirect administration pages to site’s original domain (remote login disabled if this redirect is disabled)”

This is a very big problem, could you help me ?
Thanks

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