一个php会话变量导致重定向的取消设置会话

I am using a combination of Javascript and PHP Facebook sdk to integrate the log in to my website (hosted on localhost).

The code after Facebook initialization and getting the access token:

if(fbidExists($profile['id']) == true)
  {

    $query = "SELECT userid AS id, username FROM users WHERE fbid = ".   $profile['id'] ;

    $login = mysqli_fetch_assoc(mysqli_query($GLOBALS['connection'], $query));

    $_SESSION['id'] = $login['id'];
    $_SESSION['username'] = $login['username'];

    header("Location: http:\\\\localhost\website\\");
    exit();
  }

Problem: After redirect there are no session variables whenever I use $login['username'], otherwise the session variables are transferring.

If I change the SQL query and replace username by any other column there is no problem and I can see the session variables after redirect. For example : $query = "SELECT userid AS id, email FROM users WHERE fbid = ". $profile['id'] ; $_SESSION['username'] = $profile['email'] creates no problem

The $_SESSION['username'] variable can be easily set through other files and creates no problem (when i use it with my own log in)

username in MySQL is of varchar type and I am using session_start() on every page and exit() after header.

Thanks for all your help. Turns out it was a problem because in the second script one on the variables was not set which was destroying the session.