Php Yardım

Selam arkadaşlar,

Hazır almış olduğum bi sciptte sunucu tarafında "Url kısmından bu sayfaya erişiminiz yasak" hatası alıyrum. Script localhostta hiç problemsiz çalışıyor.

Scriptın ürün detay ve alt kategori sayfaları şöyle

urun_altkat.php
<?php $u1=mysql_query("select * from urunler where urun_altkat='$altkat'");
while($u2=mysql_fetch_assoc($u1)) {
?>
<div class="grid_8 alpha" style=" float:left; width:350px; background-position: 10% 50%; margin-top:5px; padding-right:120px;">

<p><a class="zoom" href="Admin/upload/<?php echo $u2['resim']; ?>" rel="prettyPhoto[gallery1]">
<img src="Admin/upload/<?php echo $u2['resim']; ?>" width="350" height="220" title="<?php echo $u2['urun_adi']; ?> " alt="<?php echo $u2['urun_adi']; ?>"></img></a></p>
<hr class="grid_12 alpha">
</div>

<div class="grid_4 omega" style="float:left; margin-left:-100px; margin-top:4px;">
<h4><a href="urun-detay.php?id=<?php echo $u2['urun_id']; ?>"><?php echo $u2['urun_adi']; ?></a></h4>

<?php echo $u2['urun_altkat']; ?><br>
<p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><br><br>

<a class="button" href="urun-detay.php?id=<?php echo $u2['urun_id']; ?>">Ürün Özellikleri</a>
</div>
<?php } ?>
<?php $u1=mysql_query("select * from urunler where urun_altkat='$altkat'");
while($u2=mysql_fetch_assoc($u1)) {
?>
<div class="grid_8 alpha" style=" float:left; width:350px; background-position: 10% 50%; margin-top:5px; padding-right:120px;">

<p><a class="zoom" href="Admin/upload/<?php echo $u2['resim']; ?>" rel="prettyPhoto[gallery1]">
<img src="Admin/upload/<?php echo $u2['resim']; ?>" width="350" height="220" title="<?php echo $u2['urun_adi']; ?> " alt="<?php echo $u2['urun_adi']; ?>"></img></a></p>
<hr class="grid_12 alpha">
</div>

<div class="grid_4 omega" style="float:left; margin-left:-100px; margin-top:4px;">
<h4><a href="urun-detay.php?id=<?php echo $u2['urun_id']; ?>"><?php echo $u2['urun_adi']; ?></a></h4>

<?php echo $u2['urun_altkat']; ?><br>
<p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><br><br>

<a class="button" href="urun-detay.php?id=<?php echo $u2['urun_id']; ?>">Ürün Özellikleri</a>
</div>
<?php } ?>

urun-detay.php
<?php
error_reporting(1);
$id=mysql_real_escape_string($_GET["id"]);
include("Admin/include/ayar.php");

$listele2 = mysql_query("Select * from basliklar");
$sql2 = mysql_fetch_array($listele2);
$menu = mysql_query("select * from menuler");
$menuu = mysql_fetch_array($menu);

$bas=mysql_query("select * from urunler where urun_id='$id'"); $basy=mysql_fetch_assoc($bas);

if (mysql_num_rows($bas) <= 0)
{
header("Location: index.php");
}
else
{
//mysql_fetch_array
}
$listele = mysql_query("Select * from seo");
$sql = mysql_fetch_array($listele);
?>
<?php $h=mysql_query("select * from urunler where urun_id='$id' "); $hy=mysql_fetch_assoc($h); ?>
<!--project info-->
<div id="project" class="grid_4 alpha">
<?php


$art = $id + 1 ;
$eksi = $id - 1 ;

?>
<span class="next right"><a class="fancy_link" href="urun-detay.php?id=<?php echo $art; ?>">İleri</a></span>
<span class="back left"><a class="fancy_link" href="urun-detay.php?id=<?php echo $eksi; ?>">Geri</a></span>
<ul>
<li><h4>Ürün Özellikleri</h4></li>
<li><br>
<?php echo $hy['ozellikler']; ?></li>

</ul>
</div>
<!--end project info-->
<?php

if ($id == null)
{



echo "<script>alert('Url kısmından bu sayfaya erişiminiz yasak')</script>";
header("Location: index.php");
die();


}
?>

<!--project picture-->

<div class="grid_8 portfolio omega">
<p><?php

if ($hy['resim'] == null ){

echo "Ürün Görseli Girilmemiştir.";
die();
}else{
?>
<a class="zoom" href="Admin/upload/<?php echo $hy['resim']; ?>" rel="prettyPhoto[gallery1]"><img src="Admin/upload/<?php echo $hy['resim']; ?>" title="<?php echo $hy['urun_adi'];?>" width="626" alt="#"></a>
</p><?php }

?>
</div>
</div>
</div>
</div>

bi yardımcı olurmusunuz.

if ($id == null) aratıp if ($id == "") yaparmısınız ?