Ошибка "Имя типа . отсутсвует в типе ." - C#

var vkUser = new Vk.Vk("Василий Пупкин", 22, 987);

var facebookUser = new Fb.Fb("Геннадий Петров", 28, 56);

var twitterUser = new Tw.Tw("Елизавета Короткевич", 18, 99);

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Kursovaya
{
    class Program
    {
        static void Main(string[] args)
        {
            var vkUser = new Vk.Vk("Василий Пупкин", 22, 987);
            var facebookUser = new Fb.Fb("Геннадий Петров", 28, 56);
            var twitterUser = new Tw.Tw("Елизавета Короткевич", 18, 99);
 
            UserProfile.PrintUserInfo(new VkAdapter(vkUser));
            UserProfile.PrintUserInfo(new FbAdapter(facebookUser));
            UserProfile.PrintUserInfo(new TwAdapter(twitterUser));
            Console.Read();
        }
        public class Vk : IVk
        {
            private readonly string _vkName;
            private readonly int _vkAge;
            private readonly int _vkNumberOfFriends;
 
            public Vk(string vkName, int vkAge, int vkNumberOfFriends)
            {
                _vkName = vkName;
                _vkAge = vkAge;
                _vkNumberOfFriends = vkNumberOfFriends;
            }
 
            public string VkName
            {
                get { return _vkName; }
            }
            public int VkAge
            {
                get { return _vkAge; }
            }
            public int VkNumberOfFriends
            {
                get { return _vkNumberOfFriends; }
            }
        }
        
        public class Tw : ITw
        {
            private readonly string _twName;
            private readonly int _twAge;
            private readonly int _twNumberOfFriends;
 
            public Tw(string twName, int twAge, int twNumberOfFriends)
            {
                _twName = twName;
                _twAge = twAge;
                _twNumberOfFriends = twNumberOfFriends;
            }
 
            public string TwName
            {
                get { return _twName; }
            }
            public int TwAge 
            {
                get { return _twAge; }
            }
            public int VkNumberOfFriends 
            {
                get { return _twNumberOfFriends; }
            }
        }
        public class Fb : IFb
        {
            private readonly string _fbName;
            private readonly int _fbAge;
            private readonly int _fbNumberOfFriends;
 
            public Fb(string fbName, int fbAge, int fbNumberOfFriends)
            {
                _fbName = fbName;
                _fbAge = fbAge;
                _fbNumberOfFriends = fbNumberOfFriends;
            }
 
            public string FbName
            {
                get { return _fbName; }
            }
            public int FbAge
            {
                get { return _fbAge; }
            }
            public int FbNumberOfFriends
            {
                get { return _fbNumberOfFriends; }
            }
        }
 
        public interface IAdapter
        {
            string Name { get; }
            int Age { get; }
            int NumberOfFriends { get; }
        }
 
        class VkAdapter : IAdapter
        {
            private readonly IVk _vk;
 
            public VkAdapter(IVk vk)
            {
                _vk = vk;
            }
 
            public string Name
            {
                get { return _vk.VkName; }
            }
            public int Age
            {
                get { return _vk.VkAge; }
            }
            public int NumberOfFriends
            {
                get { return _vk.VkNumberOfFriends; }
            }
        }
 
        class TwAdapter : IAdapter
        {
            private readonly ITw _tw;
 
            public TwAdapter(ITw tw)
            {
                _tw = tw;
            }
 
            public string Name
            {
                get { return _tw.TwName; }
            }
            public int Age
            {
                get { return _tw.TwAge; }
            }
            public int NumberOfFriends
            {
                get { return _tw.VkNumberOfFriends; }
            }
        }
 
        class FbAdapter : IAdapter
        {
            private readonly IFb _fb;
 
            public FbAdapter(IFb fb)
            {
                _fb = fb;
            }
 
            public string Name
            {
                get { return _fb.FbName; }
            }
            public int Age
            {
                get { return _fb.FbAge; }
            }
            public int NumberOfFriends
            {
                get { return _fb.FbNumberOfFriends; }
            }
        }
 
        public static class UserProfile
        {
            public static void PrintUserInfo(IAdapter user)
            {
                Console.WriteLine("Имя пользователя: \t\t {0}", user.Name);
                Console.WriteLine("Возраст: \t\t\t {0}", user.Age);
                Console.WriteLine("Количество друзей: \t\t {0}", user.NumberOfFriends);
                Console.WriteLine("--- --- --- --- --- ---");
            }
        }
    }
}