Probleme mysql_num_rows(): [Résolu]

j'ai un probleme en niveau mysql_num_rows():
<?php
$PremiereFois=!isset($_POST["b1"]);
$MotDePasseOK=false;
$LoginOK=false;
if (!$PremiereFois)
{
$pseudo=$_POST["lg"];
$pwd=$_POST["motdepass"];
$connection=mysql_connect("localhost","root") or die("Pb. connexion serveur");
$bd=mysql_select_db("art",$connection) or die("Pb. base de données");
$sql="select pwd from user where lg='$pseudo'";
$query=mysql_query($sql,$connection);
$nb=mysql_num_rows($query);
if ($nb==1) $LoginOK=true;
if ($LoginOK)
{
$e=mysql_fetch_row($query);
if ($e[0]==$pwd)
{
$MotDePasseOK=true;
setcookie("lg",$pseudo);
header("Location:enchere.php");
}
}
}
?>