Починил.
Причиной оказалось вот что:
Изначально магазин инсталлился версии 1,5,3. Потом пришлось версию откатить до 1,5,1,3
Убил полностью всю таблицу order и вставил в мускуль этот код:
DROP TABLE IF EXISTS `oc_order`;
CREATE TABLE `oc_order` (
`order_id` int(11) NOT NULL AUTO_INCREMENT,
`invoice_no` int(11) NOT NULL DEFAULT '0',
`invoice_prefix` varchar(26) COLLATE utf8_general_ci NOT NULL,
`store_id` int(11) NOT NULL DEFAULT '0',
`store_name` varchar(64) COLLATE utf8_general_ci NOT NULL,
`store_url` varchar(255) COLLATE utf8_general_ci NOT NULL,
`customer_id` int(11) NOT NULL DEFAULT '0',
`customer_group_id` int(11) NOT NULL DEFAULT '0',
`firstname` varchar(32) COLLATE utf8_general_ci NOT NULL DEFAULT '',
`lastname` varchar(32) COLLATE utf8_general_ci NOT NULL,
`email` varchar(96) COLLATE utf8_general_ci NOT NULL,
`telephone` varchar(32) COLLATE utf8_general_ci NOT NULL DEFAULT '',
`fax` varchar(32) COLLATE utf8_general_ci NOT NULL DEFAULT '',
`shipping_firstname` varchar(32) COLLATE utf8_general_ci NOT NULL,
`shipping_lastname` varchar(32) COLLATE utf8_general_ci NOT NULL DEFAULT '',
`shipping_company` varchar(32) COLLATE utf8_general_ci NOT NULL,
`shipping_address_1` varchar(128) COLLATE utf8_general_ci NOT NULL,
`shipping_address_2` varchar(128) COLLATE utf8_general_ci NOT NULL,
`shipping_city` varchar(128) COLLATE utf8_general_ci NOT NULL,
`shipping_postcode` varchar(10) COLLATE utf8_general_ci NOT NULL DEFAULT '',
`shipping_country` varchar(128) COLLATE utf8_general_ci NOT NULL,
`shipping_country_id` int(11) NOT NULL,
`shipping_zone` varchar(128) COLLATE utf8_general_ci NOT NULL,
`shipping_zone_id` int(11) NOT NULL,
`shipping_address_format` text COLLATE utf8_general_ci NOT NULL,
`shipping_method` varchar(128) COLLATE utf8_general_ci NOT NULL DEFAULT '',
`payment_firstname` varchar(32) COLLATE utf8_general_ci NOT NULL DEFAULT '',
`payment_lastname` varchar(32) COLLATE utf8_general_ci NOT NULL DEFAULT '',
`payment_company` varchar(32) COLLATE utf8_general_ci NOT NULL,
`payment_address_1` varchar(128) COLLATE utf8_general_ci NOT NULL,
`payment_address_2` varchar(128) COLLATE utf8_general_ci NOT NULL,
`payment_city` varchar(128) COLLATE utf8_general_ci NOT NULL,
`payment_postcode` varchar(10) COLLATE utf8_general_ci NOT NULL DEFAULT '',
`payment_country` varchar(128) COLLATE utf8_general_ci NOT NULL,
`payment_country_id` int(11) NOT NULL,
`payment_zone` varchar(128) COLLATE utf8_general_ci NOT NULL,
`payment_zone_id` int(11) NOT NULL,
`payment_address_format` text COLLATE utf8_general_ci NOT NULL,
`payment_method` varchar(128) COLLATE utf8_general_ci NOT NULL DEFAULT '',
`comment` text COLLATE utf8_general_ci NOT NULL,
`total` decimal(15,4) NOT NULL DEFAULT '0.0000',
`reward` int(8) NOT NULL,
`order_status_id` int(11) NOT NULL DEFAULT '0',
`affiliate_id` int(11) NOT NULL,
`commission` decimal(15,4) NOT NULL,
`language_id` int(11) NOT NULL,
`currency_id` int(11) NOT NULL,
`currency_code` varchar(3) COLLATE utf8_general_ci NOT NULL,
`currency_value` decimal(15,8) NOT NULL,
`date_added` datetime NOT NULL,
`date_modified` datetime NOT NULL,
`ip` varchar(15) COLLATE utf8_general_ci NOT NULL DEFAULT '',
PRIMARY KEY (`order_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci;