Facebook connect and post php

i've got this php code that uses macbook sdk4 to publish post in user's wall, but it doesn't work. it gives me this error when i try to login:

Fatal error: Uncaught exception 'Facebook\FacebookClientException' with message 'Duplicate status message' in /membri/bestparty/APP/facebook/src/Facebook/FacebookRequestException.php:122 Stack trace: #0 /membri/bestparty/APP/facebook/src/Facebook/FacebookRequest.php(268): Facebook\FacebookRequestException::create('{"error":{"mess...', Object(stdClass), 500) #1 /membri/bestparty/APP/facebook/fbconfig.php(43): Facebook\FacebookRequest->execute() #2 {main} thrown in /membri/bestparty/APP/facebook/src/Facebook/FacebookRequestException.php on line 122

this is the code

<?php
session_start();
// added in v4.0.0
require_once 'autoload.php';
require 'functions.php';
use Facebook\FacebookSession;
use Facebook\FacebookRedirectLoginHelper;
use Facebook\FacebookRequest;
use Facebook\FacebookResponse;
use Facebook\FacebookSDKException;
use Facebook\FacebookRequestException;
use Facebook\FacebookAuthorizationException;
use Facebook\GraphObject;
use Facebook\Entities\AccessToken;
use Facebook\HttpClients\FacebookCurlHttpClient;
use Facebook\HttpClients\FacebookHttpable;
// init app with app id and secret
FacebookSession::setDefaultApplication( 'xxx','xxx' );
$required_scope     = 'public_profile, publish_actions, email, manage_pages'; //Permissions required
// login helper with redirect_uri
    $helper = new FacebookRedirectLoginHelper('http://ift.tt/1yVTdGL' );
try {
  $session = $helper->getSessionFromRedirect();

} catch( FacebookRequestException $ex ) {
  // When Facebook returns an error
} catch( Exception $ex ) {
  // When validation fails or other local issues
}
// see if we have a session
if ( isset( $session ) ) {
  // graph api request for user data
  $request = new FacebookRequest( $session, 'GET', '/me' );
  $response = $request->execute();
  // get response
  $graphObject = $response->getGraphObject();
        $fbid = $graphObject->getProperty('id');              // To Get Facebook ID
        $fbfullname = $graphObject->getProperty('name'); // To Get Facebook full name
        $femail = $graphObject->getProperty('email');   

      // TRY PUBLISH    
  $postrequest = new FacebookRequest( $session, 'POST', '/me/feed', array('message' => 'Ho appena scaricato DONUT, provala anche tu!'));
  $postresponse = $postrequest->execute();
  $posting = $postresponse->getGraphObject();
  echo $posting->getProperty('id');


    /* ---- Session Variables -----*/
        $_SESSION['FBID'] = $fbid;           
        $_SESSION['FULLNAME'] = $fbfullname;
        $_SESSION['EMAIL'] =  $femail;
         checkuser($fbid,$fbfullname,$femail);
    /* ---- header location after session ----*/


        $cookie_name = 'FBID';
        $cookie_value = $fbid;
        setcookie($cookie_name, $cookie_value, time() + (86400 * 30), '/'); 
        $cookie_name2 = 'FULLNAME';
        $cookie_value2 = $fbfullname;
        setcookie($cookie_name2, $cookie_value2, time() + (86400 * 30), '/'); 


        /*echo" <script type=\"text/javascript\">
            function goBack() {
            javascript: history.go(-1);
            }
            window.onload=goBack;
      </script>";*/                  /*PROVA PER LOCALE TORNARE INDIETRO HISTORY*/

      header("Location: ../loginpage.php");

} else {

  $cookie_name = 'FBID';
        $cookie_value = $fbid;
        setcookie($cookie_name, $cookie_value, time() + (86400 * 30), '/'); 
  $loginUrl = $helper->getLoginUrl( array( 'scope' => $required_scope ) );


  header("Location: ".$loginUrl);
}
?>

if i delete the user's post it works fine:

      // TRY PUBLISH    
  $postrequest = new FacebookRequest( $session, 'POST', '/me/feed', array('message' => 'Ho appena scaricato DONUT, provala anche tu!'));
  $postresponse = $postrequest->execute();
  $posting = $postresponse->getGraphObject();
  echo $posting->getProperty('id');

so i think that the problem is on it, but where?

and also, how can i do to post on user wall from another page without login request another time?

and the last question is, why cookies aren't stored when i close the browser?