asp

请高手指点：为什么会出现错当前上下文中不存在名称“File”
using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Data.SqlClient;
public partial class WebUserControl : System.Web.UI.UserControl
{
    protected void Page_Load(object sender, EventArgs e)
    {    }
    protected void SureBtn_Click(object sender, EventArgs e)
    {
        if (FileName.Text.Trim() != "")
        {
            if ((upfile.PostedFile.ContentLength > 0) && (upfile.ToString()!=""))
            {
                String fileName = upfile.PostedFile.FileName.Substring(
                    upfile.PostedFile.FileName.LastIndexOf("\\"),
                    upfile.PostedFile.FileName.Length
                    - upfile.PostedFile.FileName.LastIndexOf("\\"));
                String fileTime = DateTime.Now.Year.ToString()
                    + DateTime.Now.Month.ToString() + DateTime.Now.Day.ToString()
                    + DateTime.Now.Hour.ToString()
                    + DateTime.Now.Second.ToString()
                    + DateTime.Now.Minute.ToString()
                    + DateTime.Now.Millisecond.ToString();
                fileName = "\\" + fileTime + GetRandomint()
                    + fileName.Substring(fileName.IndexOf("."), fileName.Length
                    - fileName.IndexOf("."));
                if (File.Exists(Server.MapPath(Request.ApplicationPath) + "\\UpLoads" + fileName) == false)
                {
                    try
                    {
                        upfile.PostedFile.SaveAs(Server.MapPath(Request.ApplicationPath) + "\\UpLoads" + fileName);
                        FileDB file = new FileDB();
                        file.AddFile(FileName.Text.Trim(), "\\UpLoads" + fileName, upfile.PostedFile.ContentType);
                        sucessMassage.Visible = true;
                    }
                    catch
                    {
                        sucessMassage.Visible = true;
                        sucessMassage.Text = "由于网络原因，上载文件错误";
                    }
                    FileName.Text = "";
                }
                else 
                { 
                    sucessMassage.Visible   =   true; 
                    sucessMassage.Text   =   "你上载文件的文件名称已经存在，请更改你的文件名称！ "; 
                } 
            }
            else 
            { 
                sucessMassage.Visible   =   true; 
                sucessMassage.Text   =   "文件的内容不能为空！ "; 
            } 
               
        }
        else 
        { 
            sucessMassage.Visible   =   true; 
            sucessMassage.Text   =   "文件的名称不能为空！ "; 
        } 
    }
    private String GetRandomint()
    {
        Random random = new Random();
        return(random.Next(10000).ToString());
    }
}