c# - 此类不支持此方法错误@client.DownloadFile

Question

我突然说这个奇怪的错误System.Net.WebException : The request was abborted: The Request was canceled. ---> System.NotSupportedException : This method is not supported by this class。我不知道为什么会发生，因为它曾经可以正常工作。

我尝试在网上搜索，但在这件事上没有找到任何帮助。以下是我使用的方法，我已经指出了给出错误的行。

    //get column heading names from formatted text file
    public string getFTextColumnHead(string serverURL, string userName, string password, int headRow,
                                     string filePath, string reqFrom)
    {
        string line = "";
        //initialize WebClient object
        WebClient client = new WebClient();
        //if the request is for web
        if (reqFrom == "web")
        {
            //send web request to retreive the data from the url
            HttpWebRequest req = (HttpWebRequest) WebRequest.Create(serverURL);
            //parse credentials to the web server to authenticate
            client.Credentials = new NetworkCredential(userName, password);
            //Grab Data from the web server and save to the given path
            client.DownloadFile(new Uri(serverURL), filePath);//<---exception occurs here
        }
        //initialize input output stream and open the downloaded file
        StreamReader file = new StreamReader(filePath);
        //loop through the rows of the file until the column heading row is reached
        for (int i = 0; i < headRow; i++)
        {
            //read the line
            line = file.ReadLine();
        }
        //dipoase the client
        client.Dispose();
        //return the column heading string
        return line;
    }

感谢你们。我即将结束这个项目的最后期限。这一切都发生在最后一刻。非常感谢您的帮助:)

PS我安装Resharper以查看代码。但我没有对这个特定的班级做出任何建议:)。