WebException when trying to use WebClient with Delicious API

When trying to use Delicious API to get users bookmarks I get WebException saying "The remote server returned an error: NotFound.". I have looked and I can't find any more details about the problem.

Here is the code that I am using. Do someone know what can be wrong?

string fullUrl = "https://api.del.icio.us/v1/posts/al开发者_运维技巧l?";
WebClient client = new WebClient();
client.Credentials = new System.Net.NetworkCredential(Username, Password);
client.Headers[HttpRequestHeader.UserAgent] = "DeliciousWindowsPhoneClient";
client.DownloadStringAsync(new Uri(fullUrl));
client.DownloadStringCompleted += (object sender, DownloadStringCompletedEventArgs e) => {
    if (e.Error == null)
    {
        XDocument xmlDocument = XDocument.Parse(e.Result);
        callback(new DownloadXmlCompletedArgs(e) { Xml = xmlDocument });
    }
    else
    {
        callback(new DownloadXmlCompletedArgs(e));
    }
    lastConnectTime = System.DateTime.Now;
};

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It is the server responding with an error, not found. Have you double-checked the URL ? Try visiting it in a browser.

If the browser works, and the code does not, try narrowing down the differences between the requests being sent. Perhaps the server requires a specific header or a cookie to allow you access ? A good tool for narrowing this down is Fiddler.