Voice Recognition grammar problem

I have already posted in the forum, I just figure out there is this section, sorry for repost.

I'm trying to implement Voice Recognition inside Unity. I had tried the Keyboard emulation solution made by ZJP, and is very a nice application, but my idea was using the windows System.Speech.dll to call the speech recognition from inside the project.

So I copied System.Speech.dll inside the asset folder and I wrote down the simple code below, follow the MSDN sample

However there is some problem with this Grammar g = new Grammar (gb);

Error :

MissingMethodException: Method not found: 'System.Reflection.MethodInfo.op_Inequality'. System.Speech.Recognition.Grammar.LoadAndCompileCfgData (Boolean isImportedGrammar, Boolean stgInit) System.Speech.Recognition.Grammar.InitialGrammarLoad (System.String ruleName, System.Object[] parameters, Boolean isImportedGrammar) System.Speech.Recognition.Grammar..ctor (System.Speech.Recognition.GrammarBuilder builder) TTSUnityWin.Start () (at Assets/TTSUnityWin.cs:52)

 using UnityEngine;
 using System.Collections;
 using SpeechLib;
 using System.Xml;
 using System.IO;
 using System.Speech.Recognition;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Reflection;
 using System ;
  
 using System.Speech.AudioFormat;
 using System.Speech.Recognition.SrgsGrammar;
 using System.Speech.Synthesis; //need later
 using System.Speech.Synthesis.TtsEngine;
  
 public class TTSUnityWin : MonoBehaviour {
    
     void sr_SpeechRecognized(object sender, SpeechRecognizedEventArgs e)
     {
  
         print ("something");
     }
  
     void Start(){
  
         SpeechRecognizer sr = new SpeechRecognizer ();
         sr.SpeechRecognized += new EventHandler<SpeechRecognizedEventArgs>(sr_SpeechRecognized);
  
  
         Choices colori = new Choices();
             colori.Add (new string[] {"red","green","blue"});
             GrammarBuilder gb = new GrammarBuilder ();
             //gb.Culture = new CultureInfo("en-US");
             //gb.Culture = new System.Globalization.CultureInfo (1033);
             gb.Append (colori);
             Grammar g = new Grammar (gb);
             //sr.RequestRecognizerUpdate();
  
  
             sr.LoadGrammar(g);
  
     }
    
     // Update is called once per frame
     void Update()
     {
         if (Input.GetKeyDown(KeyCode.Space))
         {
    
         //DO NOTHING :)
        
         }
     }
 }