Не устанавливается Tickets

Could not create table `modx_tickets_views` SQL: CREATE TABLE `modx_tickets_views` (`parent` INT(10) unsigned NOT NULL DEFAULT '0', `uid` INT(10) unsigned NOT NULL DEFAULT '0', `guest_key` CHAR(32) NULL, `timestamp` DATETIME NOT NULL, PRIMARY KEY (`parent`,`uid`,`guest_key`)) ENGINE=MyISAM ERROR: Array ( [0] => 42000 [1] => 1171 [2] => All parts of a PRIMARY KEY must be NOT NULL; if you need NULL in a key, use UNIQUE instead )