Speech recognizer can't recognise some words !

private void cmdEnable_Click(object sender, System.EventArgs e)//button to start recognizer
{
    if (xpmode)
    {
//ignore this because these code is for window xp

    }
    else
    {
        if (!recInited)
        {
//if the button is click the first time, init variables 
            recognizer = new SpeechRecognitionEngine();
            recognizer.SetInputToDefaultAudioDevice();
            recognizer.SpeechRecognized += new EventHandler<SpeechRecognizedEventArgs>(recognizer_SpeechRecognized);
        }
        else
        {
            if (recognizer != null)
            {
//stop the old recognizer for new grammars defined in the textbox
                recognizer.RecognizeAsyncStop();
            }
        }
        changerecDict();
        recognizer.RecognizeAsync(RecognizeMode.Multiple);//TurnSpeechRecognitionOn
        recInited = true;
    }
}
void changerecDict()
{
    recogniseDict = grammartext.Text.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
    if (xpmode)
    {
    }
    else
    {
        recognizer.UnloadAllGrammars();
        recognizer.LoadGrammar(new Grammar(new GrammarBuilder(new Choices(recogniseDict)))); //[string] contains {"one","two","three","car","book"
    }
}
//event 4 xp
private void Reco_Event(int StreamNumber, object StreamPosition,SpeechRecognitionType RecognitionType,ISpeechRecoResult Result)
{
//ignore
}
//event 4 7
private void recognizer_SpeechRecognized(object sender, SpeechRecognizedEventArgs e)
{
    txtReco.Text = e.Result.Text + " " + e.Result.Confidence;
}