Try the DocumentCompleted
Event:
webBrowser.DocumentCompleted +=
new WebBrowserDocumentCompletedEventHandler(webBrowser_DocumentCompleted);
void webBrowser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
webBrowser.Document.GetElementById("product").SetAttribute("value", product);
webBrowser.Document.GetElementById("version").SetAttribute("value", version);
webBrowser.Document.GetElementById("commit").InvokeMember("click");
}