When I try to logout of the session I created I keep getting modify header errors.. Here is my code

```
   function logout()
 {
   $this->session->unset_userdata('logged_in');
   session_destroy();
   redirect('home', 'refresh');
 }

```

Here are the errors:

```
A PHP Error was encountered

Severity: Warning

Message: Cannot modify header information - headers already sent by (output started at /Users/Rob/stage/dashboard.php:36)

Filename: libraries/Session.php

Line Number: 688

A PHP Error was encountered

Severity: Warning

Message: Cannot modify header information - headers already sent by (output started at /Users/Rob/stage/dashboard.php:36)

Filename: helpers/url_helper.php

Line Number: 540

```

Any ideas what would cause this? 

This is my entire controller for the the code.

```
<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
session_start(); //we need to call PHP's session object to access it through CI
class dashboard extends CI_Controller {

 function __construct()
 {
   parent::__construct();
 }

 function index()
 {
   if($this->session->userdata('logged_in'))
   {
     $session_data = $this->session->userdata('logged_in');
     $data['username'] = $session_data['username'];
     $this->load->view('dashboard', $data);
   }
   else
   {
     //If no session, redirect to login page
     redirect('login', 'refresh');
   }
 }

 function logout()
 {
   $this->session->unset_userdata('logged_in');
   session_destroy();
   redirect('home', 'refresh');
 }

}

?>

```

I basically just log the user into a view and then there is a logout link on that page which when they click it they then get logged out of the session which then runs the logout function. Any ideas?