Petit probleme de php

salut a tous jai telecharger un cite en zip sur supportduweb.com et la jai une erreur le site cest un forum mais la page daccueil a des erreur php
voila le code ou elle indique
<?php
$dn1 = mysql_query('select c.id, c.name, c.description, c.position, (select count(t.id) from topics as t where t.parent=c.id and t.id2=1) as topics, (select count(t2.id) from topics as t2 where t2.parent=c.id and t2.id2!=1) as replies from categories as c group by c.id order by c.position asc');
$nb_cats = mysql_num_rows($dn1);
while($dnn1 = mysql_fetch_array($dn1))
{
?>
et voila lerreur
Nouvelle Catégorie
Warning: mysql_num_rows() expects parameter 1 to be resource, boolean given in C:\wamp\www\ok\Forum\index.php on line 71

Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given in C:\wamp\www\ok\Forum\index.php on line 72
et mem lorsque je creer une nouvelle categorie sa ne saffiche pas
merci davance