当我使用web服务调用时，遇到了"500内部服务器错误"的问题。是什么原因导致这个问题？如何解决？
请给我建议。
这是我的代码：
MailMessage objEmail = new MailMessage(new MailAddress(ConfigurationManager.AppSettings["emailAdd"].ToString()), new MailAddress(ConfigurationManager.AppSettings["emailAdd"].ToString()));
objEmail.Subject = "Test";
objEmail.Body = "EJSCODE:" + _Message;
objEmail.Priority = MailPriority.High;
SmtpClient SmtpMail = new SmtpClient();
SmtpMail.Host = "localhost";
SmtpMail.DeliveryMethod = SmtpDeliveryMethod.PickupDirectoryFromIis;
SmtpMail.PickupDirectoryLocation = @"C:\Inetpub\wwwroot\MailMsg2";
SmtpMail.Send(objEmail);