Update:
Following the Wordpress guide (and Osclass has a very similar structure of files/folders), i REMOVED the ZB BLOCK line of php code from Theme's "head.php".
I added that line to "oc-load.php" and "config.php". Be carefull to add the line to the very top, and not to add any space or line feed.
Until now i see no problems and ZB BLOCK works very well.
I will keep you updated. Keep in mind that ZB BLOCK keeps out also SPAMMERS by IPs.
(still not sure if the change of config.php is needed, and _maybe_ ZB BLOCK is called twice ?)