An unhandled exception of type 'System.Exception' occurred in HtmlAgilityPack.dll

I am trying to use HTMLAgilityPack with VS2008/.Net 3.5. I get this error

An unhandled exception of type 'System.Exception' occurred in HtmlAgilityPack.dll

Additional information: You need to set UseIdAttribute property to true to enable this feature

This is the code;

public string kmail = "deneme";
    public string ksifre = "deneme123";
    private void button2_Click(object sender, EventArgs e)
    {

        HtmlAgilityPack.HtmlDocument doc = new HtmlAgilityPack.HtmlDocument();
        doc.GetElementbyId("username_or_email").SetAttributeValue("Value", kmail);//bilgileri gir
        doc.GetElementbyId("password").SetAttributeValue("Value", ksifre);
        HtmlElement button = Browser.Document.GetElementById("allow");//tıkla
        button.InvokeMember("click");
    }

I tryed old versions of DLL but didn't worked.

How can I fix this issue? Thanks.