PHP Warning: Missing argument 1 for pun_htmlspecialchars

Solved:
The lines 147-149 (OLD)

// START SUBST - <pun_title>
$tpl_main = str_replace('<pun_title>', '<h1><span>'.pun_htmlspecialchars().'</span></h1>', $tpl_main);
// END SUBST - <pun_title>

I changed to :

// START SUBST - <pun_title>
$tpl_main = str_replace('<pun_title>', '<h1><span>'.pun_htmlspecialchars($pun_config['']).'</span></h1>', $tpl_main);
// END SUBST - <pun_title>

Indeed, all you're doing that way is adding an empty h1 and span (and, if PunBB was using E_ALL, I think that would give a notice).

First off it is not mine forum, I don't know what the forum owner has done with all files etc.

I asked for help to remove the error message, nothing else. The error message is gone now. And now I can check the config if needed. all PHP error reporting is on and no error is reported. I know there is a empty tag but that one doesn't fill up discspace with error logs.