我有如下功能并出现错误String could not be parsed as XML
$category_feed_url = "http://www.news4u.com/blogs/category/articles/feed/";
$file = file_get_contents($category_feed_url);
$xml = new SimpleXMLElement($file);
foreach($xml->channel->item as $feed)
{
echo $feed->link;
echo $feed->title;
...
为什么会发生此错误。