C# flash 图片上传出现 “文件上传过程中出现I/O错误”

前台WebForm1.aspx页面：
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="Web.User.WebForm1" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

后台WebForm1.aspx.cs页面：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace Web.User
{
public partial class WebForm1 : System.Web.UI.Page
{
protected string avatarFlashParam;
protected string EncodeLocalhost;
protected string Localhost;
protected string uid;
protected void Page_Load(object sender, EventArgs e)
{
int port = HttpContext.Current.Request.Url.Port;
string ApplicationPath = HttpContext.Current.Request.ApplicationPath != "/" ? HttpContext.Current.Request.ApplicationPath : string.Empty;
uid = "1";
Localhost = string.Format("{0}://{1}{2}{3}",
HttpContext.Current.Request.Url.Scheme,
HttpContext.Current.Request.Url.Host,
(port == 80 || port == 0) ? "" : ":" + port,
ApplicationPath);
EncodeLocalhost = HttpUtility.UrlEncode(Localhost);
avatarFlashParam = string.Format("{0}/image/common/camera.swf?nt=1&inajax=1&appid=1&input={1}&ucapi={2}/PhotoAjax.ashx", Localhost, uid, EncodeLocalhost);
}
}
}

PhotoAjax页面：
<%@ WebHandler Language="C#" Class="PhotoAjax" %>

using System;
using System.Web;
using System.IO;

public class PhotoAjax : IHttpHandler
{

public void ProcessRequest(HttpContext context)
{
    string uid = context.Request.QueryString["input"];
    if (!string.IsNullOrEmpty(context.Request["Filename"]) && !string.IsNullOrEmpty(context.Request["Upload"]))
    {
        ResponseText(UploadTempAvatar(uid));
    }
    if (!string.IsNullOrEmpty(context.Request["avatar1"]) && !string.IsNullOrEmpty(context.Request["avatar2"]) && !string.IsNullOrEmpty(context.Request["avatar3"]))
    {
        CreateDir(uid);
        if (!(SaveAvatar("avatar1", uid) && SaveAvatar("avatar2", uid) && SaveAvatar("avatar3", uid)))
        {
            File.Delete(GetMapPath("..\\image\\upload\\idcardphoto\\" + uid + ".jpg"));
            ResponseText("<?xml version=\"1.0\" ?><root><face success=\"0\"/></root>");
            return;
        }
        File.Delete(GetMapPath("..\\image\\upload\\idcardphoto\\" + uid + ".jpg"));
        ResponseText("<?xml version=\"1.0\" ?><root><face success=\"1\"/></root>");
        return;
    }
}

public bool IsReusable
{
    get
    {
        return false;
    }
}

private void CreateDir(string uid)
{
    string avatarDir = string.Format("../image/upload/idcardphoto/{0}",
         uid);
    if (!Directory.Exists(GetMapPath(avatarDir)))
        Directory.CreateDirectory(GetMapPath(avatarDir));
}

private void ResponseText(string text)
{
    HttpContext.Current.Response.Clear();
    HttpContext.Current.Response.Write(text);
    HttpContext.Current.Response.End();
}

private string UploadTempAvatar(string uid)
{
    string filename = uid + ".jpg";
    string uploadUrl = GetRootUrl("../image/") + "upload/idcardphoto";
    string uploadDir = GetMapPath("..\\image\\upload\\idcardphoto");
    if (!Directory.Exists(uploadDir + "temp\\"))
        Directory.CreateDirectory(uploadDir + "temp\\");

    filename = "temp/" + filename;
    if (HttpContext.Current.Request.Files.Count > 0)
    {
        HttpContext.Current.Request.Files[0].SaveAs(uploadDir + filename);
    }

    return uploadUrl + filename;
}

private byte[] FlashDataDecode(string s)
{
    byte[] r = new byte[s.Length / 2];
    int l = s.Length;
    for (int i = 0; i < l; i = i + 2)
    {
        int k1 = ((int)s[i]) - 48;
        k1 -= k1 > 9 ? 7 : 0;
        int k2 = ((int)s[i + 1]) - 48;
        k2 -= k2 > 9 ? 7 : 0;
        r[i / 2] = (byte)(k1 << 4 | k2);
    }
    return r;
}

private bool SaveAvatar(string avatar, string uid)
{
    byte[] b = FlashDataDecode(HttpContext.Current.Request[avatar]);
    if (b.Length == 0)
        return false;
    string size = "";
    if (avatar == "avatar1")
        size = "large";
    else if (avatar == "avatar2")
        size = "medium";
    else
        size = "small";
    string avatarFileName = string.Format("../image/upload/idcardphoto/{0}/{1}.jpg",
        uid, size);
    FileStream fs = new FileStream(GetMapPath(avatarFileName), FileMode.Create);
    fs.Write(b, 0, b.Length);
    fs.Close();
    return true;
}

public static string GetRootUrl(string forumPath)
{
    string ApplicationPath = HttpContext.Current.Request.ApplicationPath != "/" ? HttpContext.Current.Request.ApplicationPath : string.Empty;
    int port = HttpContext.Current.Request.Url.Port;
    return string.Format("{0}://{1}{2}{3}/{4}",
                         HttpContext.Current.Request.Url.Scheme,
                         HttpContext.Current.Request.Url.Host,
                         (port == 80 || port == 0) ? "" : ":" + port,
                         ApplicationPath,
                         forumPath);
}

public static string GetMapPath(string strPath)
{
    if (HttpContext.Current != null)
    {
        return HttpContext.Current.Server.MapPath(strPath);
    }
    else //非web程序引用
    {
        strPath = strPath.Replace("/", "\\");
        if (strPath.StartsWith("\\"))
        {
            strPath = strPath.Substring(strPath.IndexOf('\\', 1)).TrimStart('\\');
        }
        return System.IO.Path.Combine(AppDomain.CurrentDomain.BaseDirectory, strPath);
    }
}

}

我在网上找的一个flash图片上传，我拿到自己的程序里之后上传图片就提示如下错误，找了半天没找到原因：

具体到哪一步出错？