Session variable not passing between pages

Question

Hi, I've got a form that calculates checkbox values and puts them in a total field called txtTotal. When the user clicks send, I need to pass the total to a payment page.  The form page has PHP
session_start();
$_SESSION['sessTotal'] = $_POST['txtTotal'];
and the payment page has
session_start(); at the top of the page and <?php echo $_SESSION['sessTotal']; ?> where I want the total to display. The total does not carry over to the payment page and I can't work out why.
Here is all the PHP from the form page as I'm pretty new to PHP and not sure if there's a conflict (should session_start appear more than once?)  Thanks guys
<?php require_once('Connections/df.php'); ?>
<?php
//initialize the session
if (!isset($_SESSION)) {
session_start();
$_SESSION['sessTotal'] = $_POST['txtTotal'];
// ** Logout the current user. **
$logoutAction = $_SERVER['PHP_SELF']."?doLogout=true";
if ((isset($_SERVER['QUERY_STRING'])) && ($_SERVER['QUERY_STRING'] != "")){
  $logoutAction .="&". htmlentities($_SERVER['QUERY_STRING']);
if ((isset($_GET['doLogout'])) &&($_GET['doLogout']=="true")){
  //to fully log out a visitor we need to clear the session varialbles
  $_SESSION['MM_Username'] = NULL;
  $_SESSION['MM_UserGroup'] = NULL;
  $_SESSION['PrevUrl'] = NULL;
  unset($_SESSION['MM_Username']);
  unset($_SESSION['MM_UserGroup']);
  unset($_SESSION['PrevUrl']);
  $logoutGoTo = "index.php";
  if ($logoutGoTo) {
    header("Location: $logoutGoTo");
    exit;
?>
<?php
if (!isset($_SESSION)) {
  session_start();
$MM_authorizedUsers = "";
$MM_donotCheckaccess = "true";
// *** Restrict Access To Page: Grant or deny access to this page
function isAuthorized($strUsers, $strGroups, $UserName, $UserGroup) {
  // For security, start by assuming the visitor is NOT authorized.
  $isValid = False;
  // When a visitor has logged into this site, the Session variable MM_Username set equal to their username.
  // Therefore, we know that a user is NOT logged in if that Session variable is blank.
  if (!empty($UserName)) {
    // Besides being logged in, you may restrict access to only certain users based on an ID established when they login.
    // Parse the strings into arrays.
    $arrUsers = Explode(",", $strUsers);
    $arrGroups = Explode(",", $strGroups);
    if (in_array($UserName, $arrUsers)) {
      $isValid = true;
    // Or, you may restrict access to only certain users based on their username.
    if (in_array($UserGroup, $arrGroups)) {
      $isValid = true;
    if (($strUsers == "") && true) {
      $isValid = true;
  return $isValid;
$MM_restrictGoTo = "index.php";
if (!((isset($_SESSION['MM_Username'])) && (isAuthorized("",$MM_authorizedUsers, $_SESSION['MM_Username'], $_SESSION['MM_UserGroup'])))) {  
  $MM_qsChar = "?";
  $MM_referrer = $_SERVER['PHP_SELF'];
  if (strpos($MM_restrictGoTo, "?")) $MM_qsChar = "&";
  if (isset($_SERVER['QUERY_STRING']) && strlen($_SERVER['QUERY_STRING']) > 0)
  $MM_referrer .= "?" . $_SERVER['QUERY_STRING'];
  $MM_restrictGoTo = $MM_restrictGoTo. $MM_qsChar . "accesscheck=" . urlencode($MM_referrer);
  header("Location: ". $MM_restrictGoTo);
  exit;
?>
<?php
if (!function_exists("GetSQLValueString")) {
function GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "")
  if (PHP_VERSION < 6) {
    $theValue = get_magic_quotes_gpc() ? stripslashes($theValue) : $theValue;
  $theValue = function_exists("mysql_real_escape_string") ? mysql_real_escape_string($theValue) : mysql_escape_string($theValue);
  switch ($theType) {
    case "text":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;   
    case "long":
    case "int":
      $theValue = ($theValue != "") ? intval($theValue) : "NULL";
      break;
    case "double":
      $theValue = ($theValue != "") ? doubleval($theValue) : "NULL";
      break;
    case "date":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;
    case "defined":
      $theValue = ($theValue != "") ? $theDefinedValue : $theNotDefinedValue;
      break;
  return $theValue;
$colname_userDets = "-1";
if (isset($_SESSION['MM_Username'])) {
  $colname_userDets = $_SESSION['MM_Username'];
mysql_select_db($database_df, $df);
$query_userDets = sprintf("SELECT usersId, userName, password, name FROM users WHERE userName = %s", GetSQLValueString($colname_userDets, "text"));
$userDets = mysql_query($query_userDets, $df) or die(mysql_error());
$row_userDets = mysql_fetch_assoc($userDets);
$totalRows_userDets = mysql_num_rows($userDets);
?>

Answer 1

OK I got it.  I needed 
session_start();
$_SESSION['sessTotal'] = $_POST['txtTotal'];
on the payments page as well, not just session_start();