Fatal error – cannot redeclare class

PHP Fatal error: Cannot declare class WP_DB_Table, because the name is already in use in /home/*/public_html/wp-content/plugins/wp-user-manager/includes/abstracts/abstract-wp-db-table.php on line 30

This class declaration from developer jjj is not inside a class_exist conditional. So this will fatal with all other plugins using the same utility class.

So, please either use a namespace or put it inside an if.