C#

private Image DownloadImage(string _URL)
{
    try
    {
        WebClient client = new WebClient();
        Stream stream = client.OpenRead(_URL); //The problem seems to be here
        Image img = Image.FromStream(stream);
        stream.Flush();
        stream.Close();
        return img;
    }
    catch (Exception e)
    {
        MessageBox.Show(e.Message);
        return null;
    }

}

private Dictionary<Type, List<Action<object>>> internalList;

public void Register<T>(Action<T> callback)
{
    Type messageType = typeof(T);
    List<Action<T>> list;

    if (internalList == null)
    {
        internalList = new Dictionary<Type, List<Action<object>>>();
    }

    if (!internalList.ContainsKey(messageType))
    {
        list = new List<Action<T>>();
        internalList.Add(messageType, list);
    }
    else
    {
        list = internalList[messageType];
    }

    list.Add(callback);
}

internalList.Add(messageType, list);

list = internalList[messageType];

List<Action<object>>