title: The URI prefix is not recognized OnDownloadStringCompleted
body: <p>I've got a problem with simply method whch gets string from asp.net 4 ashx. I'm running below methods from silverlight application which is being hosted by this asp.net application.</p>
  
  <pre><code>private void LoadPlugins()
  {
      var serviceAddress = _baseAddress
          + "PluginsService.ashx?"
          + DateTime.Now.Ticks;
  
      var client = new WebClient();
      client.DownloadStringCompleted += client_DownloadStringCompleted;
      client.DownloadStringAsync(new Uri(serviceAddress));
  }
  
  void client_DownloadStringCompleted(
      object sender,
      DownloadStringCompletedEventArgs e)
  {
      var plugins = e.Result.Split(
          new string[] { Environment.NewLine },
          StringSplitOptions.RemoveEmptyEntries);
      foreach (var plugin in plugins)
      {
          AddXap(_baseAddress + plugin);
      }
  }
  </code></pre>
  
  <p>PluginsService.ashx.cs:</p>
  
  <pre><code>namespace MefPlugins.Web
  {
      /// &lt;summary&gt;
      /// Summary description for PluginsService
      /// &lt;/summary&gt;
      public class PluginsService : IHttpHandler
      {
          private const string PluginsFolderName = "Plugins/";
  
          public void ProcessRequest(HttpContext context)
          {
              //var pluginFolder = new DirectoryInfo(
              //    HttpContext.Current.Server.MapPath(
              //    PluginsFolderName));
              //var response = new StringBuilder();
  
              //if (pluginFolder.Exists)
              //{
              //    foreach (var xap in pluginFolder.GetFiles("*.xap"))
              //    {
              //        response.AppendLine(
              //            PluginsFolderName + xap.Name);
              //    }
              //}
  
              var response = new StringBuilder();
              response.Append("test");
              context.Response.ContentType = "text/plain";
              context.Response.Write(response);
          }
  
          public bool IsReusable
          {
              get
              {
                  return false;
              }
          }
      }
  }
  </code></pre>
  
  <p>I get an error:</p>
  
  <p>System.Reflection.TargetInvocationException was unhandled by user code
    Message=An exception occurred during the operation, making the result invalid.  Check InnerException for exception details.
    StackTrace:
         w System.ComponentModel.AsyncCompletedEventArgs.RaiseExceptionIfNecessary()
         w System.Net.DownloadStringCompletedEventArgs.get_Result()
         w MefPlugins.MainPage.client_DownloadStringCompleted(Object sender, DownloadStringCompletedEventArgs e)
         w System.Net.WebClient.OnDownloadStringCompleted(DownloadStringCompletedEventArgs e)
         w System.Net.WebClient.DownloadStringOperationCompleted(Object arg)
    InnerException: System.Net.WebException
         Message=An exception occurred during a WebClient request.
         InnerException: System.NotSupportedException
              Message=The URI prefix is not recognized.
              StackTrace:
                   w System.Net.WebRequest.Create(Uri requestUri)
                   w System.Net.WebClient.GetWebRequest(Uri address)
                   w System.Net.WebClient.DownloadStringAsync(Uri address, Object userToken)
              InnerException: </p>
  
  <p>Where could be a bug? this is an example from <a href="http://www.galasoft.ch/sl4u/code/chapter20/20.02-Mef/MefPlugins.zip" rel="nofollow">http://www.galasoft.ch/sl4u/code/chapter20/20.02-Mef/MefPlugins.zip</a></p>