请高手帮我看看这个错误

floatld 2003-10-17 09:40:02

<%@ Page language="c#" %>
<%@ Import Namespace="System.Web"%>
<%@ Import Namespace="System.Web.Mail"%>
<HTML>
<body>
<script language="C#" runat="server" id="SCRIPT1">
public void SendMail(Object Obj,EventArgs e)
{
MailMessage mailobj =new MailMessage();
mailobj.From=mailfrom.Text;
mailobj.To=to.Text;
mailobj.Cc=cc.Text;
// mailobj.Bcc=bcc.Text;
mailobj.Subject=mailsubject.Text;
mailobj.Body=mailbody.Text;
mailobj.BodyFormat=MailFormat.Html;
//mailObj.BodyEncoding=MailFormat.Base64;
mailobj.Priority=MailPriority.High;
//mailobj.Attachments.Add(new MailAttachment("c:\\Boot.ini"));

String filename = attach.PostedFile.FileName;
if (filename!="")
mailobj.Attachments.Add(new MailAttachment(filename));
SmtpMail.SmtpServer="mail.jlu.edu.cn";
SmtpMail.Send(mailobj);
panelSendMail.Visible=false;
panelMailSent.Visible=true;

}
</script>
<center><h2>使用asp.net发送电子邮件</h2>
</center>
<center><h3>编写日期：2001年WTO Entry</h3>
</center>
<asp:Panel ID="panelSendMail" runat="server" Width="371px">
<asp:label id="Headingmsg" runat="server" Text="输入您的邮件地址:"></asp:label>
<FORM id="form1" method="post" runat="server">
<P>发送给：
<asp:textbox id="to" runat="server"></asp:textbox><BR>
抄送给email:
<asp:textbox id="cc" runat="server"></asp:textbox><BR>
发送者email:
<asp:textbox id="mailfrom" runat="server"></asp:textbox><BR>
主题:
<asp:textbox id="mailsubject" runat="server"></asp:textbox>
</P>
<P>附件：<BR>
<INPUT id="attach" type="file" runat="server"></P>
<FONT face="宋体"></FONT>
<P>
<asp:TextBox id="mailbody" runat="server" Height="157px" Width="296px" TextMode="Multiline"></asp:TextBox></P>
<P><FONT face="宋体"></FONT><FONT face="宋体"></FONT><BR>
<asp:button id="submit" onclick="SendMail" runat="server" text="立即发送 "></asp:button></P>
</FORM>
</asp:Panel>
<asp:Panel ID="panelMailSent" Runat="server" Visible="False">
发送成功
</asp:Panel>
</body>
</HTML>
错误：

未将对象引用设置到对象的实例。
说明: 执行当前 Web 请求期间，出现未处理的异常。请检查堆栈跟踪信息，以了解有关该错误以及代码中导致错误的出处的详细信息。

异常详细信息: System.NullReferenceException: 未将对象引用设置到对象的实例。

堆栈跟踪:

[NullReferenceException: 未将对象引用设置到对象的实例。]
ASP.sendmail1_aspx.SendMail(Object Obj, EventArgs e) in http://localhost/democode/sendmail/sendmail1.aspx:21
System.Web.UI.WebControls.Button.OnClick(EventArgs e)
System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument)
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument)
System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData)
System.Web.UI.Page.ProcessRequestMain()

...全文