Console.Writeline throwing error CS0234 in one class but the program.cs in the same project doesn't.

using Microsoft.AspNetCore.SignalR.Client;

namespace AJS.DVDCentral.UI.Console
{
    public class SignalRConnection
    {
        private string hubAddress;
        HubConnection _connection;

        public string User { get; set; }
        public string Message { get; set; }
        string owner;

        public SignalRConnection(string hubAddress)
        {
            this.hubAddress = hubAddress;
        }
        public SignalRConnection(string hubAddress, string owner)
        {
            this.hubAddress = hubAddress;
            this.owner = owner;
        }

        public HubConnection HubConnection
        {
            get { return _connection; }
        }

        public void Start()
        {
            _connection = new HubConnectionBuilder()
                .WithUrl(hubAddress)
                .Build();

            _connection.On<string, string>("ReceiveMessage", (s1, s2) => OnSend(s1, s2));


            _connection.StartAsync();
        }

        private void OnSend(string user, string message)
        {
            Console.WriteLine($"{user}: {message}");
            User = user;
            Message = message;
        }

        public void Stop()
        {

            _connection.StopAsync();
        }

        public void ConnectToChannel(string user)
        {
            Start();
            string message = user + " connected...";

            try
            {
                _connection.InvokeAsync("SendMessage", "System", message);

            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }
        }

        public void SendMessageToChannel(string user, string message)
        {
            try
            {
                //Start();
                //Console.WriteLine($"{user} {message}");
                _connection.InvokeAsync("SendMessage", user, message);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }

        }

    }
}

using Microsoft.AspNetCore.SignalR.Client;

namespace AJS.DVDCentral.UI.Console
{
    public class SignalRConnection
    {
        private string hubAddress;
        HubConnection _connection;

        public string User { get; set; }
        public string Message { get; set; }
        string owner;

        public SignalRConnection(string hubAddress)
        {
            this.hubAddress = hubAddress;
        }
        public SignalRConnection(string hubAddress, string owner)
        {
            this.hubAddress = hubAddress;
            this.owner = owner;
        }

        public HubConnection HubConnection
        {
            get { return _connection; }
        }

        public void Start()
        {
            _connection = new HubConnectionBuilder()
                .WithUrl(hubAddress)
                .Build();

            _connection.On<string, string>("ReceiveMessage", (s1, s2) => OnSend(s1, s2));


            _connection.StartAsync();
        }

        private void OnSend(string user, string message)
        {
            Console.WriteLine($"{user}: {message}");
            User = user;
            Message = message;
        }

        public void Stop()
        {

            _connection.StopAsync();
        }

        public void ConnectToChannel(string user)
        {
            Start();
            string message = user + " connected...";

            try
            {
                _connection.InvokeAsync("SendMessage", "System", message);

            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }
        }

        public void SendMessageToChannel(string user, string message)
        {
            try
            {
                //Start();
                //Console.WriteLine($"{user} {message}");
                _connection.InvokeAsync("SendMessage", user, message);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }

        }

    }
}