Need help (Php session)

i start a new session with : session_start();
then i set some session variable like this : $_SESSION['name']=$_POST['name'];\
and some another variables.
at bottom of page i set header to diffrent page : header('location: index.php');
exit();
now in new page (index.php i can't access to my session variables, like $_SESSION['name'])
what's wrong ?
thanks.



here is my files :

a.php

========================================

session_start();

require ('config.inc.php');
if(isset($_POST))
foreach($_POST as $v=>$k)
{
$items[$v]=$k;
}

$sql="SELECT * FROM members WHERE username='{$items['user']}' AND pass=MD5('{$items['Password']}') ";
$res=mysql_query($sql);
$row=mysql_fetch_assoc($res);
if($row['username'])
{ $_SESSION['type']=$row['type'];
$_SESSION['name']=$row['name'];
$_SESSION['family']=$row['family'];
$_SESSION['username']=$row['username'];
$_SESSION['date']=$row['date'];

}

header('location: admin.php');
exit();

======================================

admin.php

=====================================

<?php
session_start();
if(!isset($_SESSION['admin']))
{
header('location: index.php');
exit();
}
require ('config.inc.php');

?>

.

.

.

=================================