First, this may be unrelated to the problem, but it is still a problem. In this other Forum Topic you posted your server/Proxy is using an outdated Server Protocol. Server Protocol HTTP/1.0 was phased out 15 years ago in 1999. The new Server Protocol as of 1999 (15 years ago) is HTTP/1.1. Hackers and Spammers still use old software/Proxies that use Server Protocol HTTP/1.0 because that old Server Protocol allows them to do nasty things that they cannot do with the new Server Protocol HTTP/1.1. You should take care of that problem either way and update/upgrade your Proxy and configure it to use the new Server Protocol.
http://forum.ait-pro.com/forums/topic/403-error-in-security-log-monitoring-from-hoster/
For now deactivate/Turn Off the Plugin Firewall on this website.
I assume you have an Nginx frontend server/Proxy and have an Apache server handling the backend – php and htaccess? Go to the BPS Pro System Info page and post this information about your website/server:
Server Type:
Operating System:
WP Filesystem API Method:
Server API: