Authentication on google: OAuth2 keeps returning 'invalid_grant'

I started to configure google calendar on my new application. I almost made an exact copy of the authentication code displayed at google developers ( https://developers.google.com/google-apps/calendar/instantiate ), but i keep getting the following error: Error fetching OAuth2 access token, message: 'invalid_grant' I'm currently using Fork-CMS ( http://www.fork-cms.com ), a young lightweigth CMS. I correctly configured the config.php file of the google-api-php-client. (client-id, client-secret, redirect-uri, development key,...) and the redirect uri is correctly set on the google api's console. My code looks as follows: ``` <?php /** * This is a widget with a calendar implementation. * * @package frontend * @subpackage events * * @author Michiel Vlaminck <michielvlaminck@gmail.com> */ class FrontendEventsWidgetCalendar extends FrontendBaseWidget { private $events = array(); private $authUrl = array(); /** * Execute the extra * * @return void */ public function execute() { // call parent parent::execute(); // load template $this->loadTemplate(); // get data $this->getData(); // parse $this->parse(); } /** * Get the data from Google Calendar * This method is only executed if the template isn't cached * * @return void */ private function getData() { require_once PATH_LIBRARY . '/external/google-api-php-client/src/apiClient.php'; require_once PATH_LIBRARY . '/external/google-api-php-client/src/contrib/apiCalendarService.php'; $client = new apiClient(); $service = new apiCalendarService($client); if (isset($_SESSION['oauth_access_token'])) { $client->setAccessToken($_SESSION['oauth_access_token']); } else { $token = $client->authenticate(); $_SESSION['oauth_access_token'] = $token; } if ($client->getAccessToken()) { $calId = FrontendEventsModel::getCalendarId((int) $this->data['id']); $calId = $calId[0]['calendar_id']; $events = $service->events->listEvents($calId); $this->events = $events['items']; $_SESSION['oauth_access_token'] = $client->getAccessToken(); } else { $this->authUrl = $client->createAuthUrl(); } } /** * Parse * * @return void */ private function parse() { $this->tpl->assign('events', $this->events); $this->tpl->assign('authUrl', $this->authUrl); } } ?> ``` When I open this widget-page for the first time, I get directed to google to authenticate the application. When I agree, I get redirected to my application and that's the point where I'm getting: ``` apiAuthException » Main Message Error fetching OAuth2 access token, message: 'invalid_grant' File C:\wamp\www\Officevibes\library/external\google-api-php-client\src\auth\apiOAuth2.php Line 105 Date Thu, 05 Apr 2012 08:34:47 +0000 URL http://localhost/calendar?code=4/YPUpFklKvhEeTcMm4moRth3x49oe Referring URL (Unknown) Request Method GET User-agent Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.142 Safari/535.19 ```