NinjaFirewall fatal error: Cannot retrieve WordPress database credentials

Hello,
I help a friend to secure his site with NinjaFirewall and got this message. Try to use the wp-db.php, but wonder. Looks like, the script read not the actual folder.

Uploaded the script to folder for main domain and several subdomains
– maindomain.com
– sub1.maindomain.com
– sub2.maindomain.com
– backup.maindomain.com

But all resulst are for /home/httpd/vhosts/maindomain.com/backup.maindomain.com/wp-config.php. Is there a bug in this script?

thanks for help
Gerd