Silverlight REST - membership module

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C#

try
{
WebClient reportClient = new WebClient();
reportClient.Credentials = new NetworkCredential("jusankar", "jusankar123");
string reportUri = "http://xyz.com:4511/LIService.svc/GetReport";
reportClient.DownloadStringCompleted +=new DownloadStringCompletedEventHandler(reportClient_DownloadStringCompleted);
reportClient.DownloadStringAsync(new Uri(reportUri));
}
catch (Exception exp)
{
    MessageBox.Show("I am in problem");
}

It's not working, how to do?

How to pass username and password through REST type web-service and authenticate