Redirect not working

[foxwizzy]

<?php require_once('Connections/TSFH.php'); ?>
<?php
// *** Validate request to login to this site.
if (!isset($_SESSION)) {
  session_start();
}

$loginFormAction = $_SERVER['PHP_SELF'];
if (isset($_GET['accesscheck'])) {
  $_SESSION['PrevUrl'] = $_GET['accesscheck'];
}

if (isset($_POST['username'])) {
  $loginUsername=$_POST['username'];
  $password=$_POST['password'];
  $MM_fldUserAuthorization = "aclevel";
  $MM_redirectLoginSuccess = "/users/" . $loginUsername . "index.php";
  $MM_redirectLoginFailed = "/login.php";
  $MM_redirecttoReferrer = false;
  mysql_select_db($database_TSFH, $TSFH);
  	
  $LoginRS__query=sprintf("SELECT username, password, aclevel FROM users WHERE username=%s AND password=%s",
  GetSQLValueString($loginUsername, "text"), GetSQLValueString($password, "text")); 
   
  $LoginRS = mysql_query($LoginRS__query, $TSFH) or die(mysql_error());
  $loginFoundUser = mysql_num_rows($LoginRS);
  if ($loginFoundUser) {
    
    $loginStrGroup  = mysql_result($LoginRS,0,'aclevel');
    
    //declare two session variables and assign them
    $_SESSION['MM_Username'] = $loginUsername;
    $_SESSION['MM_UserGroup'] = $loginStrGroup;	      

    if (isset($_SESSION['PrevUrl']) && false) {
      $MM_redirectLoginSuccess = $_SESSION['PrevUrl'];	
    }
    header("Location: " . $MM_redirectLoginSuccess );
  }
  else {
    header("Location: ". $MM_redirectLoginFailed );
  }
}
?>

this is my login page code
if successfully login redirect to /users/$loginUsername/index.php
problem is that it redirects me to site root /index.php

[codewall]

try to echo $MM_redirectLoginSuccess to see what's the value in it.