I had this error just now too ,but now everyting is OK.
so revolution in the follow :
1.Open the My SQL database (Sorry,I only can use this database. )
2.Press the SQL button,enter these orders:
INSERT INTO `fo_plugins` (`name`,`is_installed`, `is_activated`, `priority`, `activated_on`, `activated_by_id`) VALUES
('core_dimensions', 1, 1, 0, NOW(), 1)
ON DUPLICATE KEY UPDATE id=id
INSERT INTO `fo_dimensions` (`code`,`name`,`is_root`,`is_manageable`,`allows_multiple_selection`,`defines_permissions`, `is_system`, `options`) VALUES
('feng_persons', 'People', 1, 0, 0, 1, 1,'{"useLangs":true,"defaultAjax":{"controller":"contact", "action": "init"},"quickAdd":{"formAction":"?c=contact&a=quick_add"}}' ),
('feng_users', 'Users', 1, 0, 0, 1, 1,'{"hidden":true,"defaultAjax":{"controller":"contact", "action": "init"}}')
ON DUPLICATE KEY UPDATE id=id
INSERT INTO `fo_object_types` (`name`,`handler_class`,`table_name`,`type`,`icon`,`plugin_id`) VALUES
('person', 'Contacts', 'contacts', 'dimension_object', 'contact', (SELECT `id` FROM `fo_plugins` WHERE `name`='core_dimensions')),
('user', 'Contacts', 'contacts', 'dimension_object', 'user', (SELECT `id` FROM `fo_plugins` WHERE `name`='core_dimensions')),
('company', 'Contacts', 'contacts', 'dimension_object', 'company', (SELECT `id` FROM `fo_plugins` WHERE `name`='core_dimensions'))
ON DUPLICATE KEY UPDATE id=id
3.OK,hope your FO everything OK now !