Error 1005 when creating foreign key

the following script produces an error:
error no. 1005
can't create table ... 

MySQL version: 5.0 
MySQL Query Browser version: 1.1.2


DROP TABLE IF EXISTS `hr`.`area`;
CREATE TABLE  `hr`.`area` (
  `ID` int(11) NOT NULL,
  `DESCRIPTION` varchar(100) NOT NULL,
  `STATUS` smallint(6) NOT NULL default '1',
  PRIMARY KEY  (`ID`),
  UNIQUE KEY `Index_2` (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

DROP TABLE IF EXISTS `hr`.`employee`;
CREATE TABLE  `hr`.`employee` (
  `id` int(10) unsigned NOT NULL auto_increment,
  `name` varchar(45) NOT NULL default '',
  `area` int(10) unsigned NOT NULL default '0',
  PRIMARY KEY  (`id`),
  KEY `Index_2` (`area`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

ALTER TABLE `hr`.`employee` ADD CONSTRAINT `FK_employee_1` FOREIGN KEY `FK_employee_1` (`area`)
    REFERENCES `area` (`ID`)
    ON DELETE RESTRICT
    ON UPDATE RESTRICT;


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