Pathauto changing drupal_get_path file path
Are you accessing this link from a subpage? It would seem that it is not appropriately pulling from the Drupal root when you are making the call (from a page other than the homepage).

You can use the global variable $base_path to get the Drupal root. More information on this global variable: https://api.drupal.org/api/drupal/developer%21globals.php/global/base_path/7