Why c# Web Browser control's InvokeMember("click") is not being fired?

I need to login to a web site using c# web browser control in an web application. The site has javascript redirects. When InvokeMember("click") is called, it does not fire. My code is as follows:

    public Form2()
    {
        SetBrowserFeatureControl();
        InitializeComponent();
    }

    int pages = 0;

    private void btnLoginEc_Click(object sender, EventArgs e)
    {
        pages = 1;
        webBrowser1.DocumentCompleted +=
             new WebBrowserDocumentCompletedEventHandler(DocumentCompleted);

        webBrowser1.Navigate("http://ift.tt/1o6ieYS");
        //webBrowser1.Refresh(WebBrowserRefreshOption.Completely);

    }       

    void DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
    {
        //WebBrowser webBrowser1 = sender as WebBrowser;
        if (webBrowser1.ReadyState != WebBrowserReadyState.Complete) return;

        if(pages == 1)
        {
            pages = 2;
            //login();
            HtmlElement userNameEle = webBrowser1.Document.GetElementById("pt1:username::content");
            HtmlElement passwordEle = webBrowser1.Document.GetElementById("pt1:password::content");
            HtmlElement logonButtonEle = webBrowser1.Document.GetElementById("pt1:logon");
            HtmlElement formEle = webBrowser1.Document.GetElementById("f1");

            if (userNameEle != null && passwordEle != null && logonButtonEle != null)
            {
                userNameEle.SetAttribute("Value", "username");
                passwordEle.SetAttribute("Value", "password");

                logonButtonEle.InvokeMember("click");


            }
        }
        else if(pages == 2)
        {
            pages = 3;
            //gotoData();

            HtmlElement someEle1 = webBrowser1.Document.GetElementById("pt1:it1::content");
            HtmlElement someEle2 = webBrowser1.Document.GetElementById("pt1:id1::content");
            HtmlElement verifyButtonEle = webBrowser1.Document.GetElementById("pt1:verify");

            if(someEle1 != null && someEle2 != null && verifyButtonEle != null)
            {
                someEle1.SetAttribute("Value", "somevalue");
                someEle2.SetAttribute("Value", "somevalue");
                verifyButtonEle.InvokeMember("click");

            }


        }

    }  

1. I need to login to site first (Login button is not clicked).
2. Then I put some value in the controls
3. Then Verify button needs to be clicked