android - java.io.IOException : No authentication challenges found

I am newbie to android and this is my first project on android. I am struggling with "authentication" problem for more than a day. I tried several options but none of them worked.

Basically, I want to call a REST API and get response. I am sure that there is no problem in API as I use the same one in another iOS application.

I pass authorization header but still authentication no found message is shown. I found few question on stackoverflow related to this, but some of them did not work and some does not make sense to me.

I get status code 401. I know this means either no authentication passed or if passed, then they are wrong. Here, I am sure my passed ones are correct.

Below is my code :

try {
    url = new URL(baseUrl);
}
catch (MalformedURLException me) {
     Log.e(TAG, "URL could not be parsed. URL : " + baseUrl + ". Line : " + getLineNumber(), me);
     me.printStackTrace();
}

try {
    urlConnection = (HttpURLConnection) url.openConnection();

    urlConnection.setRequestMethod(method); 
    urlConnection.setConnectTimeout(TIMEOUT * 1000);
    urlConnection.setChunkedStreamingMode(0);

    // Set HTTP headers                 
    String authString = "username:password";
    String base64Auth = Base64.encodeToString(authString.getBytes(), Base64.DEFAULT);
    urlConnection.setRequestProperty("Authorization", "Basic " + base64Auth);
    urlConnection.setRequestProperty("Accept", "application/json");
    urlConnection.setRequestProperty("Content-type", "application/json");


    if (method.equals("POST") || method.equals("PUT")) {
        // Set to true when posting data
        urlConnection.setDoOutput(true);

        // Write data to post to connection output stream
        OutputStream out = urlConnection.getOutputStream();
        out.write(postParameters.getBytes("UTF-8"));
    }


    try {
        // Get response
        in = new BufferedInputStream(urlConnection.getInputStream());
    }
    catch (IOException e) {
        Log.e(TAG, "Exception in getting connection input stream. in : " + in);
                    e.printStackTrace();
    }

    // Read the input stream that has response

    statusCode = urlConnection.getResponseCode();
    Log.d(TAG, "Status code : " + statusCode);
}
catch (ProtocolException pe) {
    pe.printStackTrace();
}
catch (IllegalStateException ie) {
    ie.printStackTrace();
}
catch (IOException e) {

    e.printStackTrace();
}   
finally {
    urlConnection.disconnect();
}

Look at screenshot of logcat :

Any help would be appreciated. Thank you.