"OnDisconnected(): no suitable method found to override" - SignalR

Question

I've been trying to implement a chat room by following the "Asp.Net SignalR Chat Room" tutorial on CodeProject (http://www.codeproject.com/Articles/562023/Asp-Net-SignalR-Chat-Room). However, I'm getting the error "Hubs.ChatHubs.OnDisconnected(): no suitable method found to override"

ChatHub class:

public class ChatHub : Hub
{
    #region Data Members

    static List<UserDetail> ConnectedUsers = new List<UserDetail>();
    static List<MessageDetail> CurrentMessage = new List<MessageDetail>();

    #endregion

    #region Methods

    public void Connect(string userName)
    {
        var id = Context.ConnectionId;


        if (ConnectedUsers.Count(x => x.ConnectionId == id) == 0)
        {
            ConnectedUsers.Add(new UserDetail { ConnectionId = id, UserName = userName });

            // send to caller
            Clients.Caller.onConnected(id, userName, ConnectedUsers, CurrentMessage);

            // send to all except caller client
            Clients.AllExcept(id).onNewUserConnected(id, userName);

        }

    }

    public void SendMessageToAll(string userName, string message)
    {
        // store last 100 messages in cache
        AddMessageinCache(userName, message);

        // Broad cast message
        Clients.All.messageReceived(userName, message);
    }

    public void SendPrivateMessage(string toUserId, string message)
    {

        string fromUserId = Context.ConnectionId;

        var toUser = ConnectedUsers.FirstOrDefault(x => x.ConnectionId == toUserId);
        var fromUser = ConnectedUsers.FirstOrDefault(x => x.ConnectionId == fromUserId);

        if (toUser != null && fromUser != null)
        {
            // send to 
            Clients.Client(toUserId).sendPrivateMessage(fromUserId, fromUser.UserName, message);

            // send to caller user
            Clients.Caller.sendPrivateMessage(toUserId, fromUser.UserName, message);
        }

    }

    public override System.Threading.Tasks.Task OnDisconnected()
    {
        var item = ConnectedUsers.FirstOrDefault(x => x.ConnectionId == Context.ConnectionId);
        if (item != null)
        {
            ConnectedUsers.Remove(item);

            var id = Context.ConnectionId;
            Clients.All.onUserDisconnected(id, item.UserName);

        }

        return base.OnDisconnected();
    }


    #endregion

    #region private Messages

    private void AddMessageinCache(string userName, string message)
    {
        CurrentMessage.Add(new MessageDetail { UserName = userName, Message = message });

        if (CurrentMessage.Count > 100)
            CurrentMessage.RemoveAt(0);
    }

    #endregion

}

Any clues as to why this is happening?

Answer 1

For version 2.1.1+ change

public override Task OnDisconnected()

to

public override Task OnDisconnected(bool stopCalled)