If your site have got the issue on registering user – when a user registered, you could not see that user on the Users Manager and could not login the site: Please resolve the issue as following
1) You can download the last version of the quickstart and re-create a new site.
2) Or here is a solution resolve issue on your current project
you come to the phpmyadmin of your host and execute the following sql:
INSERT INTO `jos_core_acl_aro_sections` (`id`, `value`, `order_value`, `name`, `hidden`) VALUES
(10, ‘users’, 1, ‘Users’, 0);
Note: please replace the jos_ prefix ( in jos_core_acl_aro_sections ) by your table’s prefix.