I would recommend you to reinstall your characters database. But however if you don't want to lose all of your data apply this query to your characters database :
DROP TABLE IF EXISTS `auction`;
CREATE TABLE `auction` (
`id` int(11) unsigned NOT NULL DEFAULT '0',
`houseid` int(11) unsigned NOT NULL DEFAULT '0',
`itemguid` int(11) unsigned NOT NULL DEFAULT '0',
`item_template` int(11) unsigned NOT NULL DEFAULT '0' COMMENT 'Item Identifier',
`itemowner` int(11) unsigned NOT NULL DEFAULT '0',
`buyoutprice` int(11) NOT NULL DEFAULT '0',
`time` bigint(40) NOT NULL DEFAULT '0',
`buyguid` int(11) unsigned NOT NULL DEFAULT '0',
`lastbid` int(11) NOT NULL DEFAULT '0',
`startbid` int(11) NOT NULL DEFAULT '0',
`deposit` int(11) NOT NULL DEFAULT '0',
PRIMARY KEY (`id`),
UNIQUE KEY `item_guid` (`itemguid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;