Members getting error message when saving posts

Hi,

On our listing website our members have their own member area which they login. Everything goes well, exacpt one major thing. When members try to save their (custom) post on the member area they get a server error.

When i deactivate the plugin the problem goes away.

I have NOT activated these options:
– WP Security -> Filesystem Security -> Disable Ability To Edit PHP Files:
– WP Security -> Filesystem Security -> Prevent Access to WP Default

Any idea where this permission error comes from?

https://www.ads-software.com/plugins/all-in-one-wp-security-and-firewall/