supplied argument is not a valid MySQL result resource

jeg får denne fejl når jeg åbner en php side:

mysql_fetch_array(): supplied argument is not a valid MySQL result resource in C:\wamp\www\mymovies_createXML.php on line 51

jeg går ud fra at jeg har misset et tegn et eller andet sted inden line 51, men jeg kan ved gud ikke se hvor og hvilket.

koden ser sådan ud:

 <?php
 
 //Connection to MySQL
 $MySQL_Host="localhost";
 $MySQL_Port="3306";
 $MySQL_User="";
 $MySQL_Passw="";
 $MySQL_Db="mymovies_pronto"; 
 
 // Function for connection to MySQL
 function connect_mysql() {global $MySQL_Host, $MySQL_User, $MySQL_Passw;
     if (! $linkid=@mysql_connect("$MySQL_Host","$MySQL_User","$MySQL_Passw")) {
         echo "Connection to MySQL failed ",$MySQL_Host,"<BR>";
         exit;
     }
     return $linkid;
 }
 
 //Connecting to Mysql
 $db_connect = connect_mysql();
 
 //Selecting MySQL database
 mysql_select_db($MySQL_Db , $db_connect);
 
 //Retrieving chains
 $sql_retrieve_chains = "SELECT collectionnumber FROM movies ORDER BY collectionnumber";
 $req_retrieve_chains = mysql_query($sql_retrieve_chains);
 
 
 //Functions and constants for XML
 define('EOL', "\r\n");
 
 function XML_entities($str)
 {
     return preg_replace(array("'&'", "'\"'"), array('&#38;', '&#34;'), $str);
 }   
 
 //Creating XML-file
 header("Content-Type: text/plain");
 
 print("<?xml version=\"1.0\" encoding=\"ISO-8859-1\"?>") . EOL;
 print("<Titles>") . EOL;
 while($data = mysql_fetch_array($req_retrieve_chains))  {
     print(" <Collection" . XML_entities($data['collectionnumber']) . "Number>") . EOL;
         $sql_retrieve_title = "SELECT collectionnumber, webid, title, aspect, standard, year, description
                                 FROM movies
                                 WHERE collectionnumber='" . $data['collectionnumber'] . "'
                 ORDER BY collectionnumber";
 
        $req_retrieve_title = mysql_query($sql_retrieve_title);
         $array_retrieve_title = mysql_fetch_array($req_retrieve_title);
         
 
             print("  <LocalTitle>" . XML_entities($array_retrieve_title['title']) . "</LocalTitle>") . EOL;
             print("  <WebServiceID>" . XML_entities($array_retrieve_title['webid']) . "</WebServiceID>") . EOL;
             print("  <AspectRatio>" . XML_entities($array_retrieve_title['aspect']) . "</AspectRatio>") . EOL;
             print("  <VideoStandard>" . XML_entities($array_retrieve_title['standard']) . "</VideoStandard>") . EOL;
             print("  <ProductionYear>" . XML_entities($array_retrieve_title['year']) . "</ProductionYear>") . EOL;
             print("  <Description>" . XML_entities($array_retrieve_title['description']) . "</Description>") . EOL;
         
     print(" </Collection" . XML_entities($data['collectionnumber']) . "Number>") . EOL;
 
 }
 print("</Titles>") . EOL;
 
 ?>