I get this error when i try and run a swf file:

Error #2044: Unhandled securityError:. text=Error #2048: Security sandbox violation: http://mysite.com/folder1/header.swf cannot load data from http://www.mysite.com/folder1/checkuserlog.php.
   at header_fla::MainTimeline/frame1()

It seems to activate the header.swf file, but doesn't go through the checkuserlog.php

checkuserlog.php:
<?php
session_start();
if ($_POST['post_code'] == "check_log") {
     if (!isset($_SESSION['id'])) {
          print "return_msg=not_logged_in";
        exit();    
     } else {
          $id = $_SESSION['id'];
          $firstname = $_SESSION['firstname'];
          print "member_id=$id&member_name=$firstname";
          exit();
     }
}
?>