No, the problem was that miniBB Manual gave the impression that set-up options.php/mysql should be erased (for security) TOO early during installation process.
But, in fact, it was still needed for completion by other scripts.
So, had to repeat the whole install, keep the setup options.php until ALL was completed, and erase it only later. That works OK.
Similar problems have apparently been faced by other people too (See elsewhere in this Forum). It might be a good suggestion to cearly explain at miniBB's Manual at what precise moment setup.options should be erased.
+ By the way, Paul, if we have to change later something in the setup of the forum, (i.e. add headers or footers, with coordinates, pex. logos, address, fax, email, etc.), how can it be done without having to re-start the whole installation process from scrap (from "point 0") ?
(It's a relevant question, and important in practice, but we should, maybe place it at new topic, to facilitate things and make this forum more useful).
Thank you for answering in the most efficient way that you can.