php / mysql - Issue when redirecting based on user_level -

i'm building control panel based on user_level. if user has level (0) can't access besides index page, level (1) can access everything.

my problem is, current code using... redirects me index page, if set user_level above 0.

code:

<?php $db_connection = new mysqli(db_host, db_user, db_pass, db_name); require_once("config/db.php");  $page_rows = results_per_page;  if (!$db_connection->set_charset("utf8")) {     $db_connection->errors[] = $db_connection->error; }  if($_session["user_level"] == 0)                 {                 header('location: index.php');                 } ?> 

and if try using following code....

<?php $db_connection = new mysqli(db_host, db_user, db_pass, db_name); require_once("config/db.php");  $page_rows = results_per_page;  if (!$db_connection->set_charset("utf8")) {     $db_connection->errors[] = $db_connection->error; }  if($_session["user_level"] == 0) {         header('location: index.php');     } else {         header('location: download.php'); ?> 

i http error 500 on download.php page.

all appreciated. (sorry 'noob' mistakes, first bigger project).

you using session like:

if($_session["user_level"] == 0) {     header('location: index.php'); } 

but session not started here. start session on first line like:

session_start(); 

only after can access session variable.