Estou usando o twitter4j para enviar um tweet do meu aplicativo. Quando invoco o método retrieveRequestToken, recebo o erro "Falha na comunicação com o provedor de serviços: nulo".

public static void askOAuth(Context context) {
    try {
        // Use Apache HttpClient for HTTP messaging
        consumer = new CommonsHttpOAuthConsumer(CONSUMER_KEY, CONSUMER_SECRET);
        provider = new CommonsHttpOAuthProvider(
                "https://api.twitter.com/oauth/request_token",
                "https://api.twitter.com/oauth/access_token",
                "https://api.twitter.com/oauth/authorize");
        String authUrl = provider.retrieveRequestToken(consumer, CALLBACK_URL);
        Toast.makeText(context, "Authorize this app!", Toast.LENGTH_LONG).show();
        context.startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse(authUrl)));
    } catch (Exception e) {
        Log.e(APP, e.getMessage());
        Toast.makeText(context, e.getMessage(), Toast.LENGTH_LONG).show();
    }
}

Obrigado