.net 利用ssl加密，密码验证smtp发送邮件

环境window2000,.net 1.1，客户端安装根证书
结果老是报The transport fail to connect to the server 错误
同样的代码在xp却没有问题，怀疑是CDOSYS.DLL的版本不同所致。

MailMessage objmail=new MailMessage();

objmail.From="testmail@test.com";
objmail.To =gogogo88@gogogo88.com;

objmail.BodyFormat = MailFormat.Html;
objmail.Subject="Subject for test"+ System.DateTime.Now.ToString();

//设置为需要用户验证
objmail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate", "1");
//设置验证用户名
objmail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusername", txtUser.Text);
//设置验证密码
objmail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendpassword", txtPwd.Text);
//设置ssl
objmail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpusessl","true");

SmtpMail.SmtpServer= txtServer.Text;

try
{
objmail.Body="Testing"+ System.DateTime.Now.ToString();
SmtpMail.Send(objmail);
MessageBox.Show("Send Email Successfully!");
}
catch(System.Exception explp)
{
MessageBox.Show(explp.InnerException.InnerException.ToString());
}