Silverlight WebClient issue when remote server is down.

Question

I am developing an application in Silverlight which communicates with a remote server over SSL, here is the code

private void button1_Click(object sender, RoutedEventArgs e)
        {
            WebClient wc = new WebClient();
            wc.DownloadStringCompleted += new DownloadStringCompletedEventHandler(wc_DownloadStringCompleted);
            wc.DownloadStringAsync(new Uri("https://192.168.3.31:8000"));
        }

        void wc_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
        {
            Console.WriteLine(e);
        }

I want to differentiate between errors when the "Server is down" and "SSL certificate is not installed on client machine", but the wc_DownloadStringCompleted shows the same message in both cases i.e. "The remote server returned an error: NotFound.". It should be different in case when SSL certificate problem occurs. I am using Visual Studio 2010 and Silverlight 4. Any help?