Ошибка  Fatal error: Uncaught exception 'Exception' with message 'Error: Unknown column 'main_category' in 'where clause'<br/>Error No: 1054<br/>SELECT category_id FROM oc_product_to_category WHERE product_id = '523' AND main_category = '1' LIMIT 1'
Решается запросом SQL
ALTER TABLE `oc_product_to_category` ADD `main_category` tinyint(1) NOT NULL DEFAULT '0';