Get Access Token with PHP Facebook SDK

Get Access Token with PHP Facebook SDK

Hi i was using following code
$facebook = new Facebook(array(
'appId' => 'appId',
'secret' => 'secret',
'fileUpload' => true
));
$facebook->setExtendedAccessToken();
$access_token = $_SESSION["fb_".$fb_appId."_access_token"];
$facebook->setAccessToken($access_token);
$accessToken = $facebook->getAccessToken();
$user_id = $facebook->getUser();
$fbuser = $user_id;
echo $accessToken ;
and was getting Access code , but all of sudden its stop coming its just
showing me my key and secret code ... i am bulding new app so i have
generated code many time a day .
am i doing something wrong or there is a limit for generating access code
in a day.
please help