This involves three steps 1) Return gracefully in UrlModule.HttpRequestHandler() instead of throwing an exception when the url cannot be found in its index 2) Return true instead of false in HasEvents() if no matching request is found in the map. This call will only happen in the first place for raced requests. 3) Return a 404 in GetEvents() if the request is not in the index, rather than a blank 200 OK. Many thanks to Tom Haines in http://opensimulator.org/mantis/view.php?id=6051 for doing some of the work on this.