Modifier des données avec php/mysql

Bonjour,

alors voici mon problème :

Page Modif_coord
--------------------
?php

session_start();
if (!isset($_SESSION['login'])) {
header ('Location: index.php');
exit();
}
$login=$_SESSION['login'];
?>
-
-
-
-
-
-
-

<form name="modif_coord" action="app_modif_coord.php" method="post">
<h3>Modifier mes coordonnées </h3>
<?php
$connection = mysql_connect("localhost","root","") or die ("couldn't
connect to server");
$db = mysql_select_db("base_pol",$connection) or die ("Couldn't select
database");
/* Selectionner ce qu'on va afficher */
$query = "SELECT * FROM patient where login_pat='".$login."'";
$result = mysql_query($query) or die ("Couldn't execute query.");
/* Afficher les résultats dans une table */
echo "<table>";

while ($row = mysql_fetch_array($result,MYSQL_ASSOC))
{
echo "<tr>\n";
echo "<th>matricule:</th>"."<td> <input type='text' name='matricule' value='{$row['mat_pat']}'></td>\n";
echo "<tr>\n";
echo "<th>Nom : </th>"."<td><input type='text' name='nom' value='{$row['nom_pat']}'></td>";
echo "<tr>\n";
echo "<th>Prenom : </th>"."<td><input type='text' name='prenom' value='{$row['prenom_pat']}'></td>";
echo "<tr>\n";
echo "<th>adresse : </th>"."<td><input type='text' name='adr' value='{$row['adr_pat']}'></td>\n";
echo "<tr>\n";
echo "<th>sexe : </th>"."<td><input type='text' name='sexe' value='{$row['sexe_pat']}'></td>\n";
echo "<tr>\n";
echo "<th>Date de naissance : </th>"."<td><input type='text' name='date_nais' value='{$row['date_nais']}'></td>\n";
echo "<tr>\n";

}
echo "</table>\n";
?>
<center><input type="submit" value="Mis à jour" class="button"/>
-------------------------------

dans la page "app_modif_coord.php" :
-----------------------------------------
<?php

session_start();
if (!isset($_SESSION['login'])) {
header ('Location: index.php');
exit();
}
$login=$_SESSION['login'];
?>
<?php

$connection = mysql_connect("localhost","root","") or die ("couldn't
connect to server");
$db = mysql_select_db("base_pol",$connection) or die ("Couldn't select
database");
/* Selectionner ce qu'on va afficher */
$query = "SELECT mat_pat FROM patient where login_pat='".$login."'";
$result = mysql_query($query) or die ("Couldn't execute query.");
while ($row = mysql_fetch_array($result,MYSQL_ASSOC))
{
$ancien="{$row['mat_pat']}";

}

$mat=$_POST['matricule'];
$nom=$_POST['nom'];
$prenom=$_POST['prenom'];
$adr=$_POST['adr'];
$sexe=$_POST['sexe'];
$date_nais=$_POST['date_nais'];

$req = "UPDATE patient SET mat_pat='$mat' , nom_pat='$nom' , prenom_pat='$prenom' , adr_pat='$adr' , sexe_pat='$sexe' ,
date_nais='$date_nais' WHERE mat_pat='$ancien'";

include('profil_pat.php');

?>
-----------------------------------------

Bon le problème est : A session had already been started - ignoring session_start()
!!!
aidez-moi SVP
<config>Windows XP / Safari 534.30</config>