文件上传工作在本地主机，但不是godaddy服务器(dnn网站)

我创建了一个在本地发送带有附件的电子邮件的模块，它工作正常，但在Web服务器（godaddy）上不工作。我犯了这个错误。

出现严重错误。空路径名不合法。

private void SendEmailNotification2()
{
    string to = "careers@domain.com";
    string from = "job@hotmail.com";
    string subject = "CV from Web Site";
    string body = "New CV from Web Site";
    using (MailMessage mm = newMailMessage(txtEmail.Text, "careers@domain.com"))
    {
        mm.Subject = "ssss";
        mm.Body = "baaa";
        if (FileUpload1.HasFile)
        {
            string FileName = Path.GetFileName(FileUpload1.PostedFile.FileName);
            mm.Attachments.Add(newAttachment(FileUpload1.PostedFile.InputStream, FileName));
        }
        mm.IsBodyHtml = false;
        SmtpClient smtp = newSmtpClient();
        smtp.Host = "smtp.gmail.com";
        smtp.EnableSsl = true;
        ServicePointManager.ServerCertificateValidationCallback = delegate(object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) { returntrue; };
        NetworkCredential NetworkCred = newNetworkCredential("job111@gmail.com", "Password");
        smtp.UseDefaultCredentials = true;
        smtp.Credentials = NetworkCred;
        smtp.Port = 587;
        smtp.Send(mm);
        // ClientScript.RegisterStartupScript(GetType(), "alert", "alert('Email sent.');", true);
    }
}