ผมเขียนฟังก์ชั่นแล้วขึ้น error รบกวนชึ้แนะด้วยน่ะครับ

        private string FindSizefwp(string argPahtfwd)
        {
            string[] GetFilefwp = Directory.GetFiles(argPahtfwd);
            foreach (string Filefwp in GetFilefwp)
            {
                if (Filefwp == "xxx.exe")
                {
                    FileInfo FileLenfwp = new FileInfo(Filefwp);
                    int lFileSizefwp = 0;
                    lFileSizefwp = Convert.ToInt32(FileLenfwp.Length);
                    string SizeFifwp = formatSize(lFileSizefwp);
                    return SizeFifwp;
                }
            }
            return string.Empty;
        }
        // OR
        private string FindSizefwp(string argPahtfwd)
        {
            string SizeFifwp = string.Empty;
            string[] GetFilefwp = Directory.GetFiles(argPahtfwd);
            foreach (string Filefwp in GetFilefwp)
            {
                if (Filefwp == "xxx.exe")
                {
                    FileInfo FileLenfwp = new FileInfo(Filefwp);
                    int lFileSizefwp = 0;
                    lFileSizefwp = Convert.ToInt32(FileLenfwp.Length);
                    SizeFifwp = formatSize(lFileSizefwp);
                    break;
                }
            }
            return SizeFifwp;
        }

   
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
     
            string tempStr = Server.MapPath(@"~\");
            tempStr = FindSizefwp(tempStr);
            Response.Write(tempStr);
        }
        //LiteralWriteTable(4);
    }

    private string FindSizefwp(string argPahtfwd)
    {
        string SizeFifwp = string.Empty;
        string[] GetFilefwp = Directory.GetFiles(argPahtfwd);
        foreach (string Filefwp in GetFilefwp)
        {

            string tempStr = Filefwp.Substring(Filefwp.LastIndexOf("\\") + 1);
            if (tempStr.ToLower().Equals("web.config"))
            {
                FileInfo FileLenfwp = new FileInfo(Filefwp);
                int lFileSizefwp = 0;
                lFileSizefwp = Convert.ToInt32(FileLenfwp.Length);
                SizeFifwp = formatSize(lFileSizefwp);
                break;
            }
        }
        return SizeFifwp;
    }

    private string formatSize(int someThingHere)
    {
        return someThingHere.ToString("#,##0");
    }