Getting force close on app when trying to setText() to TextView

I made an app that controls an ScoreBoard, I worked with socketServers on my java app, and a socket on my app. The thing is that I receive data from the server, but when I'm trying to set it to a TextView the app force closes. Here's the code, I very new to android/Java programming I don't know if working with AsyncTask causes the issue.

private class SendMessage extends AsyncTask<Void, Void, Void> {

    @Override
    protected Void doInBackground(Void... params) {
        try {
            client = new Socket("192.168.11.23", 4444);
            printwriter = new PrintWriter(client.getOutputStream(), true);
            printwriter.write(message);
            printwriter.flush();

            InputStream is = client.getInputStream();
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            score = br.readLine();
            Log.i("TEST", "--> " + score + " <--");
            redScore.setText(score);
            client.close();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}