Не выходит зацепить базу огненнной птицы. или баян про mscorlib 4.0.0.0 - C#

Не удалось загрузить тип \"System.Runtime.CompilerServices.ExtensionAttribute\" из сборки \"mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO; // чтоб пути до файлов проверять
//-----------------------------------------------------------------------------
using FirebirdSql.Data.FirebirdClient; // задействуем возможности агонь-птицы
using FirebirdSql.Data.Isql;
//-----------------------------------------------------------------------------
 
namespace fb_test
{
    class Program
    {
        static void Main(string[] args)
        {
            //Some constant parameters used to form up the connection string... 
            #region constant literals 
            const String User = "eorder";
            const String Password = "eorder";
            const String DBPath = "c:\\1\\eOrderClient.fdb";
            const String DLLPath = @"c:\\1\\fbclient.dll";
            const String Charset = "WIN1251";
            const int Dialect = 3;
            #endregion
 
            //I check whether we actually have a database file nearby
            //and fbembed.dll. If we don't - we leave
            if (File.Exists(DBPath) == true && File.Exists(DLLPath) == true) // чтоб все было (база и библиотека)
            {
                //I form up a connection string out of literals I've declared above
                FbConnectionStringBuilder CStr = new FbConnectionStringBuilder();
 
                CStr.ServerType = FbServerType.Embedded;
                CStr.UserID = User;
                CStr.Password = Password;
                CStr.Dialect = Dialect;
                CStr.Database = DBPath;
                CStr.Charset = Charset;
                CStr.ClientLibrary = DLLPath;
 
                //And then I finally try to connect
                FbConnection Conn = new FbConnection(CStr.ToString());
 
                try
                {
                    //See what we've got in the end
                    Console.WriteLine(CStr.ToString());
                    //And try to connect
                    Conn.Open();
                }
                catch (Exception Ex)
                {
                    //Show me what has gone wrong
                    Console.WriteLine("\n" + Ex.Message.ToString());
                    Console.ReadKey();
                }
                finally
                {
                    Conn.Close();
                }
            }
        }
    }
}