ozkan34 how did you end up with undefined in the url ? Did you click a link that contained that, or did the url change after you typed an actual discussion ID ? the normal url is /d/<discussion id>. Maybe you managed to click a link somewhere before the list of discussions were fully loaded ?
If you are refreshing (F5) the page with undefined in the url, it probably won't lead anywhere as it won't find any discussion with that ID.