Permission denied admin-ajax.php

Hi,
I’ve the following error message when I click on one of the dates of my calendar :

“Forbidden

You don’t have permission to access /wp-admin/admin-ajax.php on this server.
Apache Server at http://www.soazetline.fr Port 80″

It only works when I’m logged in my website. Can you help me ?

https://ww.wp.xz.cn/plugins/spider-event-calendar/