Magento: Compare Products link does not work

From the comments, it looks like your Magento DB does not have report_compared_product_index table.

Import the following SQL to create this table structure in your DB.

CREATE TABLE IF NOT EXISTS `report_compared_product_index` (
`index_id` bigint(20) unsigned NOT NULL COMMENT 'Index Id',
  `visitor_id` int(10) unsigned DEFAULT NULL COMMENT 'Visitor Id',
  `customer_id` int(10) unsigned DEFAULT NULL COMMENT 'Customer Id',
  `product_id` int(10) unsigned NOT NULL COMMENT 'Product Id',
  `store_id` smallint(5) unsigned DEFAULT NULL COMMENT 'Store Id',
  `added_at` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00' COMMENT 'Added At'
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COMMENT='Reports Compared Product Index Table' AUTO_INCREMENT=1 ;

ALTER TABLE `report_compared_product_index`
 ADD PRIMARY KEY (`index_id`), ADD UNIQUE KEY `UNQ_REPORT_COMPARED_PRODUCT_INDEX_VISITOR_ID_PRODUCT_ID` (`visitor_id`,`product_id`), ADD UNIQUE KEY `UNQ_REPORT_COMPARED_PRODUCT_INDEX_CUSTOMER_ID_PRODUCT_ID` (`customer_id`,`product_id`), ADD KEY `IDX_REPORT_COMPARED_PRODUCT_INDEX_STORE_ID` (`store_id`), ADD KEY `IDX_REPORT_COMPARED_PRODUCT_INDEX_ADDED_AT` (`added_at`), ADD KEY `IDX_REPORT_COMPARED_PRODUCT_INDEX_PRODUCT_ID` (`product_id`);

Let me know if this helps.