Twitter api statuses not getting

Twitter api statuses not getting

m try to use following twitter API, but unable to get user statuses. tel
me whats an error??
WebClient connectTwitter = new WebClient();
connectTwitter.DownloadStringCompleted += new
DownloadStringCompletedEventHandler(connectTwitter_DownloadStringCompleted);
connectTwitter.DownloadStringAsync(new
Uri("https://api.twitter.com/1.1/statuses/user_timeline.json?screen_name=BarackObama"));