android - Tablet (4.0.3) stops posting to server on launch while phone (2.2.3) works

I figured out that my tablet with android 4.0.3 stops here while my phone with 2.2.3 works on this code but I do not know why:

I can not think of a difference between the tablet and phone coding, someone?

/* Store this device macaddress within the server. */
    static void storeMacAddress(final Context context, final String macAddr) {
        Log.i(TAG, "Store device on Server (macAddress = " + macAddr + ")");
        String serverUrl = SERVER_URLL;
        Map params = new HashMap();
        params.put("macaddress", macAddr);
        long backoff = BACKOFF_MILLI_SECONDS + random.nextInt(1000);
        // As the server might be down, we will retry it a couple times.
        for (int i = 1; i <= MAX_ATTEMPTS; i++) {
            Log.d(TAG, "Attempt #" + i + " to store");
            try {
                post(serverUrl, params);
                Log.d(TAG, "Store op Server gelukt!");
                return;
            } catch (IOException e) {
                // Here we are simplifying and retrying on any error
                Log.e(TAG, "Failed to store on attempt " + i + ":" + e);
                if (i == MAX_ATTEMPTS) {
                    break;
                }
                try {
                    Log.d(TAG, "Sleeping for " + backoff + " ms before retry");
                    Thread.sleep(backoff);
                } catch (InterruptedException e1) {
                    // Activity finished before we complete - exit.
                    Log.d(TAG, "Thread interrupted: abort remaining retries!");
                    Thread.currentThread().interrupt();
                    return;
                }
                // increase backoff exponentially
                backoff *= 2;
            }
        }
        Log.d(TAG, "Error tijdens store op Server procedure!");
    }
private static void post(String endpoint, Map params)
            throws IOException {
        URL url;
        try {
            url = new URL(endpoint);
        } catch (MalformedURLException e) {
            throw new IllegalArgumentException("invalid url: " + endpoint);
        }
        StringBuilder bodyBuilder = new StringBuilder();
        Iterator> iterator = params.entrySet().iterator();
        // constructs the POST body using the parameters
        while (iterator.hasNext()) {
            Entry param = iterator.next();
            bodyBuilder.append(param.getKey()).append('=')
                    .append(param.getValue());
            if (iterator.hasNext()) {
                bodyBuilder.append('&');
            }
        }
        String body = bodyBuilder.toString();
        Log.v(TAG, "Posting '" + body + "' to " + url);
        byte[] bytes = body.getBytes();
        HttpURLConnection conn = null;
        try {
            Log.e("URL", "> " + url);
            conn = (HttpURLConnection) url.openConnection();
            conn.setDoOutput(true);
            conn.setUseCaches(false);
            conn.setFixedLengthStreamingMode(bytes.length);
            conn.setRequestMethod("POST");
            conn.setRequestProperty("Content-Type",
                    "application/x-www-form-urlencoded;charset=UTF-8");
            // post the request
            OutputStream out = conn.getOutputStream();
            out.write(bytes);
            out.close();
            // handle the response
            int status = conn.getResponseCode();
            if (status != 200) {
              throw new IOException("Post failed with error code " + status);
            }
        } finally {
            if (conn != null) {
                conn.disconnect();
            }
        }
      }

EDIT:
Calling from:

...
setContentView(R.layout.activity_main);
            final SharedPreferences prefs = this.getSharedPreferences("nl.easy.winkel", Context.MODE_PRIVATE);
            if(!prefs.getString("macaddress","").equals("send")) { // Send MacAddress once
                prefs.edit().putString("macaddress","send").commit();
                obtainMacAddress();
            }
and
    private void obtainMacAddress() {
            WifiManager wifiMan = (WifiManager) this.getSystemService(Context.WIFI_SERVICE);
            WifiInfo wifiInf = wifiMan.getConnectionInfo();
            String macAddr = wifiInf.getMacAddress();
            final Context context = this;
            ServerUtilities.storeMacAddress(context, macAddr + "|" + getLocalIpAddress());
    }
        public String getLocalIpAddress() {
            try {
                for (Enumeration en = NetworkInterface.getNetworkInterfaces(); en.hasMoreElements();) {
                    NetworkInterface intf = en.nextElement();
                    for (Enumeration enumIpAddr = intf.getInetAddresses(); enumIpAddr.hasMoreElements();) {
                        InetAddress inetAddress = enumIpAddr.nextElement();
                        if (!inetAddress.isLoopbackAddress()) {
                            return inetAddress.getHostAddress().toString();
                        }
                    }
                }
            } catch (SocketException ex) {
                Log.e(TAG, ex.toString());
            }
            return null;
        }

EDIT2: using AsyncTask

AsyncTask mStoreTask;
private void obtainMacAddress() {
        WifiManager wifiMan = (WifiManager) this.getSystemService(Context.WIFI_SERVICE);
        WifiInfo wifiInf = wifiMan.getConnectionInfo();
        final String macAddr = wifiInf.getMacAddress();
        final Context context = this;
        mStoreTask = new AsyncTask() {
            @Override
            protected Void doInBackground(Void... params) {
                // Store on our server
                // On server creates a new user
                ServerUtilities.storeMacAddress(context, macAddr + "|" + getLocalIpAddress());
                return null;
            }
            @Override
            protected void onPostExecute(Void result) {
                mStoreTask = null;
            }
        };
        mStoreTask.execute(null, null, null);
    }