No such file or directory in optimize

and here again a issue from admin/reports

Warning: file_get_contents(//netdna.bootstrapcdn.com/twitter-bootstrap/2.3.2/js/bootstrap.min.js): failed to open stream: No such file or directory in Drupal\Core\Asset\JsOptimizer->optimize() (Zeile 28 von /var/www/example.com/core/lib/Drupal/Core/Asset/JsOptimizer.php).

hope it helps
thanks