RDF requires PHP 5.x and SPL

AppendIterator is part of the Standard PHP Library (SPL) included in PHP 5.x by default. I can only surmise that either you are using a PHP version older than 5.0, or else SPL is, for some reason, disabled in your PHP installation. Please refer to the SPL documentation.

i am not sure, but its a web domain server so i think it shouldn't have old php.
i create a php file with phpinfo, but there is so much information http://www.co0kies.sk/abo.php
so i dont know what is wrong, i dont have problems before with CMS like wordpress, joomla etc.

line 1105 : class RDF_QueryIterator extends AppendIterator {
public function __construct() {
parent::__construct();
$this->rewind();
foreach (func_get_args() as $iterator) {
$this->append($iterator);
}
}

I had a look at your phpinfo() output, and it does look like you have PHP 5.x (there was no version information, but you had many PHP 5 extensions). However, as I guessed, it also looks like SPL isn't installed or enabled. I'm attaching a screenshot that shows how the SPL section would look on your phpinfo page.

Perhaps contact your hosting company and inquire if they could enable SPL for you? It really should not be missing in any PHP 5.x setup, as it is an essential part of PHP 5; much modern PHP software depends on it.