我有那两张table。。。

CREATE TABLE `Mail` (
`timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
`sender` varchar(255) NOT NULL DEFAULT '',
`receiver` varchar(255) NOT NULL DEFAULT '',
`text` longtext ,
PRIMARY KEY (`timestamp`,`sender`,`receiver`)
) 
ENGINE=InnoDB DEFAULT CHARSET=utf8;

... 还有。。。

CREATE TABLE `MailHeader` (
`timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
`sender` varchar(255) NOT NULL DEFAULT '',
`receiver` varchar(255) NOT NULL DEFAULT '',
`title` varchar(45) DEFAULT NULL,,
`seen` int(11) DEFAULT '0', 
`reply` int(11) DEFAULT '0',    
PRIMARY KEY (`timestamp`, `sender`, `receiver`),
CONSTRAINT `MailHeader_ibfk_1` FOREIGN KEY (
   `timestamp`, `sender`, `receiver`) REFERENCES 
   `Mail` (`timestamp`, `sender`, `receiver`)
) 
ENGINE=InnoDB DEFAULT CHARSET=utf8;

当我尝试这样更新非键列时：

UPDATE MailHeader 
SET `title` = ?, `seen` = ?, `reply` = ? 
WHERE `sender` = ? and `receiver` = ?;

我总是会犯这样的错误：
com.mysql.jdbc.exceptions.mysqlintegrityconstraintviolationexception异常：
无法添加或更新子行：外键约束失败( usr_web4930_1 . MailHeader ，约束 MailHeader_ibfk_1 外键( timestamp , sender , receiver )参考文献 Mail ( timestamp , sender , receiver )
我尝试了最简单的方法，在两个表中都有一条记录，并使用“mysql workbench”工具更改非键列。同样的错误。我真的不明白。。。