REST Service - 500 Internal Server Error

Question

I has been trying to set up a drupal REST Server in my computer (a clean drupal 6 installation). Unfortunately, I could not configure it. When I send a POST message (WITHOUT parameters);

ht.p://localhst/drupal/?q=note/note/retrieve or ht.p://localhst/drupal/?q=note/user/login, it replies 500 Internal Server Error.

I used this example (I copied and pasted the example to sites/all/modules) https://drupal.org/node/783460.

It is a drupal 6.28 in a Debian with Apache2. It has not configured clean URLs!

I am using the module Services (6.x-3.4-rc1) and Rest Server (6.x-2.0-beta3).

I checked the /var/log/apache2/error.log

[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 have another doubt, how is it possible to test these services easily? These error messages for me are not intuitive. I was using drush with watchdog but I didn't give more information.

Regards.