probleem met success op registratiepagina

<?php
include 'core/init.php';
logged_in_redirect();
include 'includes/overall/header.php'; 

if (empty($_POST) === false) {
 $required_fields = array('username', 'password', 'password_again', 'first_name', 'email');
 foreach($_POST as $key=>$value) {
  if (empty($value) && in_array($key, $required_fields) === true) {
   $errors[] = 'Fields marked with an asterisk are required';
   break 1;
  }
 }

 if (empty($errors) === true) {
  if (user_exists($_POST['username'])) {
   $errors[] = 'Sorry, the username \'' . $_POST['username'] . '\' is already taken';
  }
  if (preg_match("/\\s/", $_POST['username'] == true)) {
   $errors[] = 'Your username must not contain any spaces.';
  }
  if (strlen($_POST['password']) < 6) {
   $errors[] = 'Your password must be at least 6 characters';
  }
  if ($_POST['password'] !== $_POST['password_again']) {
   $errors[] = 'Your passwords do not match';
  }
  if (filter_var($_POST['email'], FILTER_VALIDATE_EMAIL) === false) {
   $errors[] = 'A valid email adress is required';
  }
  if (email_exists($_POST['email']) === true) {
   $errors[] = 'Sorry, the email \'' . $_POST['email'] . '\' is already in use';
  }
 }
}

?>
<h1>Register</h1>

<?php
if (isset($_GET['success']) === true && empty($_GET['success']) === false) {
 echo 'You\'ve been registered successfully! Please check your email to activate your account.';
} else {
 if (empty($_POST) === false && empty($errors) === true) {
  $register_data = array(
  'username'   => $_POST['username'],
  'password'   => $_POST['password'],
  'first_name' => $_POST['first_name'],
  'last_name'  => $_POST['last_name'],
  'email'      => $_POST['email'],
  'email_code' => md5($_POST['username'] + microtime())
  );
 
  register_user($register_data);
  header('Location: register.php?success');
  exit();
  
 } else if (empty($errors) === false) {
  echo output_errors($errors);
 }
 
 ?>
 
 <form action="" method="post">
 <ul>
 <li>
 Username*:<br>
 <input type="text" name="username">
 </li>
 <li>
 Password*:<br>
 <input type="password" name="password">
 </li>
 <li>
 Password again*:<br>
 <input type="password" name="password_again">
 </li>
 <li>
 First name*:<br>
 <input type="text" name="first_name">
 </li>
 Last name:<br>
 <input type="text" name="last_name">
 </li>
 <li>
 Email*:<br>
 <input type="text" name="email">
 </li>
 <li>
 <input type="submit" value="Register">
 </li>
 </ul>
 </form>
 <?php
}
include 'includes/overall/footer.php'; 
?>