The probem comes from your database configuration. For some reason it doesn't create Fulltext index in tables. This should be created manually. You should use phpMyAdmin database manager of your hosting service cpanel and execute this SQL:

SET SQL_MODE = "NO_AUTO_VALUE_ON_ZERO";
ALTER TABLE `apedys_wpforo_posts` ADD FULLTEXT KEY `title` (`title`);
ALTER TABLE `apedys_wpforo_posts` ADD FULLTEXT KEY `body` (`body`);
ALTER TABLE `apedys_wpforo_posts` ADD FULLTEXT KEY `title_plus_body` (`title`,`body`);
ALTER TABLE `apedys_wpforo_topics` ADD FULLTEXT KEY `title` (`title`);
ALTER TABLE `apedys_wpforo_topics` ADD FULLTEXT KEY `body` (`body`);
ALTER TABLE `apedys_wpforo_topics` ADD FULLTEXT KEY `title_plus_body` (`title`,`body`);

As far as i see your table prefix is apedys_ so I changed the SQL for you. please try to execute it again.