Also, reading the ERROR you've shared in your initial post,
Warning: include(): Failed opening '/libs/ver.inc.php' for inclusion (include_path='.:/usr/share/php') in /users/dark-poet.info/htdocs/forums/libs/ubbthreads.inc.php on line 9
it looks like you have an invalid path there:
...or whatever the correct absolute path on your server should be.
And this is the reason why your initial install would fail.