大家帮我看看JAVAMAIL的异常提示是什么意思啊(50分)

我写的代码是
message.setSubject("Test from Javamail");
message.setText("HellofromJavaMail");
编译通过，但发送时提示说邮件消息体缺少DCH，我找了帮助没发现什么是DCH，所以问问大家
javax.mail.SendFailedException: Sending failed;
nested exception is:
class javax.mail.MessagingException: IOException while sending message;
nested exception is:
javax.activation.UnsupportedDataTypeException: no object DCH for MIME ty
pe text/plain;
charset=us-ascii

抱的错是不支持的日期类型
//////发送代码
Message msg=new MimeMessage(session);
msg.setFrom(new InternetAddress(from));
InternetAddress[] address={new InternetAddress(to)};
msg.setRecipients(Message.RecipientType.TO,address);
msg.setSubject(subject);
msg.setSentDate(new Date());
////可能是你没有写这个造成的
msg.setText(body);
Transport.send(msg);