I have created a form for quick additions to database. It has the following code at the front

PHP Code:
<?php 
session_start
();
if (!isset(
$_SESSION["manager"])) {
    
header("location: admin_login.php"); 
    exit();
}
// Be sure to check that this manager SESSION value is in fact in the database
$managerID preg_replace('#[^0-9]#i'''$_SESSION["id"]); // filter everything but numbers and letters
$manager preg_replace('#[^A-Za-z0-9]#i'''$_SESSION["manager"]); // filter everything but numbers and letters
$password preg_replace('#[^A-Za-z0-9]#i'''$_SESSION["password"]); // filter everything but numbers and letters
// Run mySQL query to be sure that this person is an admin and that their password session var equals the database information
// Connect to the MySQL database  
include "../SiteScripts/connect_to_mysql.php"
$sql mysql_query("SELECT * FROM admin WHERE id='$managerID' AND username='$manager' AND password='$password' LIMIT 1"); // query the person
// ------- MAKE SURE PERSON EXISTS IN DATABASE ---------
$existCount mysql_num_rows($sql); // count the row nums
if ($existCount == 0) { // evaluate the count
     
echo "Your login session data is not on record in the database.";
     exit();
}
?>
It works fine for the first page but any other page it tells me "Your login session data is not on record in the database" If I take out the above code then it works fine. Any ideas on how to fix this issue? It use to work for all the pages but now it doesn't and I'm not sure what is wrong. Any ideas are much appreciated.