php - simplexml 'Trying to get property of non-object in' error

I'm trying to parse the XML of http://www.mpgh.net/forum/external.php?type=RSS2&forumids=175 but I get this error, can't find whats wrong.

Notice: Trying to get property of non-object in C:\xampp\htdocs\crossfire\index.php on line 9

<?php  
$rss = simplexml_load_file('http://www.mpgh.net/forum/external.php?type=RSS2&forumids=175'); 

for($i=0;$i<10;$i+=1) {
    $namespaces = $rss->getNameSpaces(true);
    $dc = $rss->children($namespaces['dc']);

    echo "Title: " . $rss->channel->item[$i]->title . "<br>";
    echo "Creator: " . $dc->channel->item[$i]->creator . "<br>";
    echo "Link: " . $rss->channel->item[$i]->link . "<br><br>";
}  
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And my second question.

Why is this code only working properly athttp://www.mpgh.net/forum/external.php?type=RSS2&forumids=175 and not at other pages likehttp://www.mpgh.net/forum/external.php?type=RSS2&forumids=168

Notice: Trying to get property of non-object in C:\xampp\htdocs\crossfire\index.php on line 7

<?php
$rss = New DOMDocument();
$rss = simplexml_load_file('http://www.mpgh.net/forum/external.php?type=RSS2&forumids=168'); 

for($i=0;$i<10;$i+=1) {

    if (substr($rss->channel->item[$i]->title, 0, 9) == '[Release]') {
        echo "Title: " . $rss->channel->item[$i]->title . "<br>";
        echo "Link: " . $rss->channel->item[$i]->link . "<br><br>";
    } else {
        echo 'Hoi<br><br>';
    }
}
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Thanks.