You have to change the require_once() in lib-common.php in any case. It should point to the same path as $_CONF['path'] (not 'path_html') , but with "config.php" attached.
$_CONF['path_html'] should point to were the lib-common.php, index.php, etc. reside. If you keep the "public_html" as part of the path, you don't need to change that variable at all.
bye, Dirk