JMAIL发送附件的问题

JMAIL版本：4.4 professional
部分代码：private void SendMail(Email email)
    {
        
        
        jmail.MessageClass myJmail = new jmail.MessageClass();
        myJmail.Charset = "GB2312";
                // 优先级
        myJmail.Priority = Convert.ToByte(1);
        myJmail.From = email.userName;
        myJmail.FromName = email.dispName;
        myJmail.Subject = email.subject;
        //身份验证的用户名
        
        myJmail.MailServerUserName = email.userName;
        myJmail.MailServerPassWord = email.pwd;        StringBuilder semail = new StringBuilder();
        semail.Append(email.body);
        
        myJmail.HTMLBody = semail.ToString();                myJmail.AddRecipient(email.addr, "", "");        try
        {
            myJmail.AddAttachment(Server.MapPath("../../images/del.gif"), false,"text/html");
            //加上附件就报错，不加正常            
            if (myJmail.Send(email.server,false))
            {
                Response.Write("成功提交至邮件服务器");
            }
            else
            {
                Response.Write("提交至邮件服务器失败");
            }
        }
        catch(Exception ex)
        {
            myJmail.Close();
            Response.Write(email.addr + " 发送失败 ");
        }
        
    }
捕获异常：Win32 Error CODE:87 参数不正确请问是什么原因造成的？