C# unity WebClient Request is not working for android build?

WebClient class is giving different result in Editor and in Android build.

    void Start () {
        path = Application.persistentDataPath;
#if UNITY_EDITOR
        path = "D:/data";
#endif

        client.DownloadProgressChanged += Progress;
        client.DownloadFileCompleted += Completed;
        client.DownloadFileAsync (new Uri(url), path+"/version");
    }

    public void Progress(object sender, DownloadProgressChangedEventArgs e)
    {
        Debug.Log(e.ProgressPercentage);
    }

    public void Completed(object sender, AsyncCompletedEventArgs e)
    {
        if (e.Error != null || e.Cancelled) {
            Debug.Log(e.Error.Message);
        } 
        else
        {
            Debug.Log("Successfully Completed");
        }
    }

When run from Unity Editor the file was downloaded fine. But when build for Android it gives a error message as Name Resolution Failure.

It gives the same error when there is no Internet Connection when running on Unity Editor. But I get the error message in Android whether the device is connected to internet or not.