LiveSDK don't work on Windows (Phone) 8.1?

I have download the version 5.6 of LiveSDK.

But this simple program don't work:

bool connected = false;
try
{
 var authClient = new LiveAuthClient();
 LiveLoginResult result = await authClient.LoginAsync(new string[] { "wl.signin", "wl.skydrive" });

 if (result.Status == LiveConnectSessionStatus.Connected)
    {
     connected = true;
     var connectClient = new LiveConnectClient(result.Session);
     var meResult = await connectClient.GetAsync("me");
     dynamic meData = meResult.Result;
    }
   }
   catch (LiveAuthException ex)
   {
    // Display an error message.
   }
   catch (LiveConnectException ex)
  {
        // Display another error message.
  }
  catch (Exception ex)
 {
}

I catch a generic Exception, obtain this exception message:

Object reference not set to an istance of an object

in row :

 LiveLoginResult result = await authClient.LoginAsync(new string[] { "wl.signin", "wl.skydrive" });

but authClient is not null. What is wrong?

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CP http://ift.tt/1lWCzDC