(CMS) login, headers already sent probleem

Hoi, Ik ben bezig met een klein CMS'je bouwen met classes, dit is voormij redelijk nieuw maar het lukt al aardig. Nu ben ik bij het inloggen aangekomen en daar krijg ik, als ik probeer in te loggen:

"Warning: Cannot modify header information - headers already sent by (output started at J:\wwwroot\cms\includes\systemcomponent.php:24) in J:\wwwroot\cms\includes\sentry.php on line 112"

Ik blijf dan ook gewoon het inlog scherm zien en word niet doorgestuurd. Nou heb ik beetje zitten proberen om het eruit te krijgen, maar ik kom er niet uit, ik hoop dat jullie me kunnen helpen. Ik zal hieronder even de desbetreffende scripts posten.

Alvast bedankt,

Bastiaan

systemcomponent

<?php
class systemcomponent
{

    var $settings;

    function getSettings()
    {

        // System variables
        $settings['siteDir'] = '';

        // Database variables
        $settings['dbhost'] = 'localhost';
        $settings['dbusername'] = 'root';
        $settings['dbpassword'] = '';
        $settings['dbname'] = 'cmsdb';

        return $settings;

    }

}
?> 

sentry

<?php
////////////////////////////////////////////////////////////////////////////////////////
// Class: sentry
// Purpose: Control access to pages
///////////////////////////////////////////////////////////////////////////////////////
class sentry
{

    var $loggedin = false; //	Boolean to store whether the user is logged in
    var $userdata; //  Array to contain user's data

    function sentry()
    {
        session_start();
        header("Cache-control: private");
    }

    //======================================================================================
    // Log out, destroy session
    function logout()
    {
        unset($this->userdata);
        session_destroy();
        return true;
    }

    //======================================================================================
    // Log in, and either redirect to goodRedirect or badRedirect depending on success
    function checkLogin($user = '', $pass = '', $group = 10, $goodRedirect = '', $badRedirect =
        '')
    {

        // Include database and validation classes, and create objects
        require_once ('dbconnector.php');
        require_once ('validator.php');
        $validate = new validator();
        $loginConnector = new dbconnector();

        // If user is already logged in then check credentials
        if ($_SESSION['user'] && $_SESSION['pass'])
        {

            // Validate session data
            if (!$validate->validateTextOnly($_SESSION['user']))
            {
                return false;
            }
            if (!$validate->validateTextOnly($_SESSION['pass']))
            {
                return false;
            }

            $getUser = $loginConnector->query("SELECT * FROM cmsusers WHERE user = '" . $_SESSION['user'] .
                "' AND pass = '" . $_SESSION['pass'] . "' AND thegroup <= " . $group .
                ' AND enabled = 1');

            if ($loginConnector->getNumRows($getUser) > 0)
            {
                // Existing user ok, continue
                if ($goodRedirect != '')
                {
                    header("Location: " . $goodRedirect . "?" . strip_tags(session_id()));
                }
                return true;
            }
            else
            {
                // Existing user not ok, logout
                $this->logout();
                return false;
            }

            // User isn't logged in, check credentials
        }
        else
        {
            // Validate input
            if (!$validate->validateTextOnly($user))
            {
                return false;
            }
            if (!$validate->validateTextOnly($pass))
            {
                return false;
            }

            // Look up user in DB
            $getUser = $loginConnector->query("SELECT * FROM cmsusers WHERE user = '$user' AND pass = PASSWORD('$pass') AND thegroup <= $group AND enabled = 1");
            $this->userdata = $loginConnector->fetchArray($getUser);

            if ($loginConnector->getNumRows($getUser) > 0)
            {
                // Login OK, store session details
                // Log in
                $_SESSION["user"] = $user;
                $_SESSION["pass"] = $this->userdata['pass'];
                $_SESSION["thegroup"] = $this->userdata['thegroup'];

                if ($goodRedirect)
                {
                    header("Location: " . $goodRedirect . "?" . strip_tags(session_id()));
                }
                return true;

            }
            else
            {
                // Login BAD
                unset($this->userdata);
                if ($badRedirect)
                {
                    header("Location:" . $badRedirect);
                }
                return false;
            }
        }
    }
}
?>