Errors while tring to use a Speech Recogniser program

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Windows.Forms;
using System.Diagnostics;
using System.Speech;
using System.Speech.Recognition;
using System.Speech.AudioFormat;
using System.Speech.Synthesis;

namespace Trying
{
    public partial class Form1 : Form
    {
        private SpeechRecognitionEngine recognitionEngine;
        public Form1()
        {
            InitializeComponent();
            try
            {
                recognitionEngine = new SpeechRecognitionEngine();
                recognitionEngine.SetInputToDefaultAudioDevice();
                recognitionEngine.SpeechRecognized += new EventHandler<SpeechRecognizedEventArgs>(recognitionEngine_SpeechRecognized);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            

            
        }

        void recognitionEngine_SpeechRecognized(object sender, SpeechRecognizedEventArgs e)
        {
            try
            {
                string line = "";
                foreach (RecognizedWordUnit word in e.Result.Words)
                {
                    if (word.Confidence >= 0.5f)
                        line += word.Text + " ";
                }
                string command = Regex.Replace(line, "Change", "");
                switch (command)
                {
                    case "Red":
                        this.BackColor = Color.Red;
                        break;
                    case "Blue":
                        this.BackColor = Color.Blue;
                        break;
                    case "Green":
                        this.BackColor = Color.Green;
                        break;
                }
                txtOutput.Text += line;//txtOutput is a RichTextBox
                txtOutput.Text += Environment.NewLine;
            }
            catch (Exception ex)
            {
                MessageBox.Show("2:" + ex.Message);
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                recognitionEngine.RecognizeAsync(RecognizeMode.Multiple);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

        private Grammar CreateGrammarObject()
        {
            try
            {
                Choices commandChoices = new Choices("Red", "Green", "Blue");
                GrammarBuilder grammarBuilder = new GrammarBuilder("Change");
                grammarBuilder.Append(commandChoices);
                Grammar g = new Grammar(grammarBuilder);
                return g;
            }
            catch (Exception ex1)
            {
                MessageBox.Show("3:" + ex1.Message);
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            recognitionEngine.RecognizeAsyncStop();
        }
    }
}