Class name must be a valid object or a string

The site totally broken, white screen and a error message.
When searched for a keyword, "Fatal error: Class name must be a valid object or a string", but only for some keywords "test", a user "daniel".
Gets a notice error in dblog, "Notice: Undefined index: controller class in entity_get_controller()" also this "Notice: Undefined property: stdClass::$entity_type in apachesolr_search_process_response()".