初始化C#的geckoWebBrowser异常

Program.cs如下：

static void Main()
    {
        Gecko.Xpcom.Initialize("D:xulrunner");
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new Form1());

    }

Form1.cs如下：

private void Form1_Load(object sender,EventArgs e)
    {
        //Gecko.Xpcom.Initialize("D:xulrunner");

        geckoWebBrowser1.Navigate("http://www.google.com");

    }

翻译自中文,例外情况如下：

“System .__ ComObject”无法转换接口类型“Gecko.nsIWebNavigation”

以下代码中抛出异常：

public ChromeContext()
{
    using (var appShallSvc = Xpcom.GetService2<nsIAppShellService>(Contracts.AppShellService))
    {
        webNav = appShallSvc.Instance.CreateWindowlessBrowser(true).AsComPtr(); //this is where the exception is thrown

        webNav.Instance.LoadURI("chrome://global/content/alerts/alert.xul",null,null);

    }

}

任何帮助将不胜感激.