Also please let me know if your website is a WP Multisite installation.
In any case you should check the attachments table in database. Use Hosting cPanel > phpMyAdmin Database manager, navigate to the WordPress database and find _wpforo_attachments table. If this table doesn't exist try to create it by executing the SQL command below in SQL tab of phpMyAdmin. Please change the red marked table prefix if your table prefix doesn't match:
CREATE TABLE IF NOT EXISTS `wp_wpforo_attachments`( `attachid` INT NOT NULL AUTO_INCREMENT, `userid` INT NOT NULL, `filename` varchar(255) NOT NULL, `fileurl` VARCHAR(255) NOT NULL, `size` INT NOT NULL DEFAULT 0, `mime` varchar(255) NOT NULL, `posts` INT NOT NULL DEFAULT 0, PRIMARY KEY (`attachid`), KEY (`posts`), KEY (`userid`) );