Problème de sessions :s

Yèp salut tout le monde,
Le problème est simple mais il incompréhensible...
Je fait un upload d'image dans un script et je veux passer une variable en session mais ca ne marche pas bien que l'upload marche..

script d'upload :

<?php
// Edit upload location here
$cheminIndex_Tmp = "./tmp/";
$destination_path = "../../tmp/";
$nomDuFichierTemp = $_FILES['myfile']['name'];
echo ("</br>nom de ufichier = ".$nomDuFichierTemp);
$fichiers_autorise = array("image/png", "image/gif", "image/png", "image/tiff", "image/jpg", "image/jpeg");

$type_file = $_FILES['myfile']['type'];
$result = 0;
$target_path = $destination_path.$nomDuFichierTemp;
if(move_uploaded_file($_FILES['myfile']['tmp_name'], $target_path)) {
$_SESSION['img']=$target_path;
$result = 1;
}



sleep(2);
?>

<script language="javascript" type="text/javascript">window.top.window.stopUpload('<?php echo $cheminIndex_Tmp.$nomDuFichierTemp."?reload=".time() ?>',' <?php echo $_FILES['myfile']['name'] ?>');</script>


l'appelle du script :

<form action=\"./gmp/model/upload.php\" method=\"post\" enctype=\"multipart/form-data\" target=\"upload_target\">
<div id=\"f1_upload_process\" name=\"f1_upload_process\" style=\"display:none;\"><img src=\"./css/images/49.gif\" /><br/>Loading...</div>
<div id=\"img_form\" name=\"f1_upload_form\" ><br/>
<input name=\"myfile\" id=\"myfile\" type=\"file\" size=\"60\" onChange=\"submit();startUpload();\"/>
</div>
<iframe id=\"upload_target\" name=\"upload_target\" src=\"#\" style=\"width:0;height:0;border:0px solid #fff;\"></iframe>

<div id=\"apercu\" style=\"display:none\">

</div>
</form>
<form action=\"index.php?action=AddPicture\" method=\"post\" name=\"AddPictureForm\">
<br/> <input type=\"submit\" name=\"Submit\" value=\"Valider\" />
</form>"


je comprend vraiment pas ... :/