403 error on sub-directory

WP on root and using you plugin, everything works great.
But today I have installed Simple Machines Forum (SMF) in a sub-directory and has a few 403 errors which disperser if I remove the .htaccess or I use default (given by host).htaccess file.
Your plugin’s settings are the cause for these errors, is there a solution?

sub-directory: mysite.com/forums

Thanks.

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