When i launch the php script, sometime works fine, but many other times it retrieve me this errror

Fatal error: Call to a member function children() on a non-object in /membri/americanhorizon/ytvideo/rilevametadatadaurlyoutube.php on line 21

This is the first part of the code

// set feed URL
$feedURL = 'http://gdata.youtube.com/feeds/api/videos/dZec2Lbr_r8';

// read feed into SimpleXML object
$entry = simplexml_load_file($feedURL);

$video = parseVideoEntry($entry);


function parseVideoEntry($entry) {      
  $obj= new stdClass;

  // get nodes in media: namespace for media information
  $media = $entry->children('http://search.yahoo.com/mrss/'); //<----this is the doomed line 21 

UPDATE: solution adopted

      for ($i=0 ; $i< count($fileArray); $i++)
  {

    // set feed URL
    $feedURL = 'http://gdata.youtube.com/feeds/api/videos/'.$fileArray[$i];


    // read feed into SimpleXML object
    $entry = simplexml_load_file($feedURL);


   if ( is_object($entry))
   {
       $video = parseVideoEntry($entry);

       echo ($video->description."|".$video->length);
       echo "<br>";
    }
     else
     {
       $i--;
     }

 }

In this mode i force the script to re-check the file that caused the error