Why does it display the error dialog when I upload it to my tablet?

public static final int NUMBER_OF_POSTS = 20;
public static final String TAG = MainListActivity.class.getSimpleName(); 
protected JSONObject mblogData;
protected ProgressBar mProgressBar;

private final String KEY_TITLE = "title";
private final String KEY_AUTHOR = "author";


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main_list);

    mProgressBar = (ProgressBar) findViewById(R.id.progressBar1);

    if(isNetworkAvailable()){
        mProgressBar.setVisibility(View.VISIBLE);

    GetBlogPostsTask getBlogPostsTask = new GetBlogPostsTask();
    getBlogPostsTask.execute();
    }
    else{
        Toast.makeText(this, "Network is down. ", Toast.LENGTH_LONG).show();
    }

}

private boolean isNetworkAvailable() {
    ConnectivityManager manager = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = manager.getActiveNetworkInfo();

    boolean isAvailable = false;{
        if(networkInfo != null && networkInfo.isConnected()){
            isAvailable = true;
        }
        return isAvailable;
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main_list, menu);
    return true;
}

public void handleBlogResponse() {
    mProgressBar.setVisibility(View.INVISIBLE);

    if(mblogData == null){
        updateDisplayForError();
    }
    else{
        try {
            JSONArray jsonPosts = mblogData.getJSONArray("posts");
            ArrayList<HashMap<String, String>> blogPosts = new ArrayList<HashMap<String, String>>();

            for(int i = 0; i < jsonPosts.length(); i++){
            JSONObject post = jsonPosts.getJSONObject(i);
            String title = post.getString(KEY_TITLE);
            title = Html.fromHtml(title).toString();

            String author = post.getString(KEY_AUTHOR);
            author = Html.fromHtml(author).toString();

            HashMap<String, String> blogPost = new HashMap<String, String>();
            blogPost.put(KEY_TITLE, title);
            blogPost.put(KEY_AUTHOR, author);

            blogPosts.add(blogPost);




            }
            String[]keys = {KEY_TITLE , KEY_AUTHOR};
            int[] ids = {android.R.id.text1, android.R.id.text2};
            SimpleAdapter adapter = new SimpleAdapter(this, blogPosts, android.R.layout.simple_list_item_2, keys, ids);
            setListAdapter(adapter);




        } catch (JSONException e) {
            Log.e(TAG, "Json Exception Found: " , e);
        }
    }
}

private void updateDisplayForError() {
    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setTitle(getString(R.string.title));
    builder.setMessage(getString(R.string.Error_Message));
    builder.setPositiveButton(android.R.string.ok, null);
    AlertDialog dialog = builder.create();
    dialog.show();

    TextView emptyTextView = (TextView) getListView().getEmptyView();
    emptyTextView.setText(getString(R.string.No_items));
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

private class GetBlogPostsTask extends AsyncTask<Object, Void, JSONObject>{

    @Override
    protected JSONObject doInBackground(Object... params) {
        int responseCode = -1;
        JSONObject jsonResponse = null;


        try {
            URL blogFeedUrl = new URL("http://blog.teamtreehouse.com/api/get_recent_summary/?count=" + NUMBER_OF_POSTS);
            HttpURLConnection connection = (HttpURLConnection) blogFeedUrl.openConnection();
            connection.connect();

            responseCode = connection.getResponseCode();
            if(responseCode == HttpURLConnection.HTTP_OK){
                InputStream inputStream = connection.getInputStream();
                Reader reader = new InputStreamReader(inputStream);
                int content = connection.getContentLength();
                char[] charArray = new char[content];
                reader.read(charArray);
                String responseData = new String(charArray);


                jsonResponse = new JSONObject(responseData);
            }

        } catch (MalformedURLException e) {
                Log.e(TAG, "Malformed URL Exception Found: " ,e );
        }
          catch(IOException e){
              Log.e(TAG, "IOExecption Found: " , e);
        }
          catch(Exception e){
              Log.e(TAG, "Exception Found: " , e );
        }
        return jsonResponse;
    }
    @Override
    protected void onPostExecute (JSONObject result){
        mblogData = result;
        handleBlogResponse();
    }
}