laravel 4 Cannot modify header information - headers already sent by (output started at

This error happened when you are using one of these statements in laravel 4 application :

 Redirect::to or  header('Location: ' . $url) 

Where your Laravel 4 application had sent a header to the screen before you decide to redirect the browser to other url . Sometimes this error caused by echo statement before the redirection , other output text or white space, But in my case the error because I have added a php closed tag:

?>  

in the end of the included files. So removing  this tag will bring the application back to normal behavior.