C-sharp Security prompts that ProtectedData does not exist in the context. - Codes Helper

C-sharp Security prompts that ProtectedData does not exist in the context.

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

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(
    Encoding.Unicode.GetString(
        System.Security.Cryptography.ProtectedData.Unprotect(
            Convert.FromBase64String(
                "...jHoAwE/Cl+sBAAAA/GdUMC8fOkSbZeHVvNAo5AAAAAAQAAAARABlAGYAYQB1AGwAdAAA......."
            ), null, System.Security.Cryptography.DataProtectionScope.LocalMachine)));
            Console.ReadLine();
        }
    }
}