REST Service - 500 Internal Server Error
The problem was when I used the drush tool. It downloaded and installed the Services module, and the Rest Server module (another no necessary module).
This error was describing this conflict between modules;

[Sun Jun 23 17:11:24.136866 2013] [:error] [pid 2957] [client::1:48424] PHP
Fatal error: Call to undefined function
services_resource_uri_formatter() in
/var/www/drupal/sites/all/modules/rest_server/includes/RESTServer.inc
on line 15

I disabled the Rest Server and restarted the HTTP server.