Error Value Array of type java.lang.String cannot be converted to JSONObject

I have a problem with parsing data to JSON php server. When i try to send the data parameter then the error appear. I see the log cat and i think the error is in the json format. But how i can change the php code or java code?

NOTE: i send latitude, longitude and a context, example: 112, 75, "work"

Log cat

04-23 21:55:01.369: ERROR/JSON Parser(415): Error parsing data org.json.JSONException: Value Array of type java.lang.String cannot be converted to JSONObject
04-23 21:55:01.421: WARN/dalvikvm(415): threadid=12: thread exiting with uncaught exception (group=0x40015560)
04-23 21:55:01.449: ERROR/AndroidRuntime(415): FATAL EXCEPTION: AsyncTask #1
04-23 21:55:01.449: ERROR/AndroidRuntime(415): java.lang.RuntimeException: An error occured while executing doInBackground()
04-23 21:55:01.449: ERROR/AndroidRuntime(415):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
04-23 21:55:01.449: ERROR/AndroidRuntime(415):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
04-23 21:55:01.449: ERROR/AndroidRuntime(415):     at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
04-23 21:55:01.449: ERROR/AndroidRuntime(415):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
04-23 21:55:01.449: ERROR/AndroidRuntime(415):     at java.util.concurrent.FutureTask.run(FutureTask.java:138)
04-23 21:55:01.449: ERROR/AndroidRuntime(415):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
04-23 21:55:01.449: ERROR/AndroidRuntime(415):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
04-23 21:55:01.449: ERROR/AndroidRuntime(415):     at java.lang.Thread.run(Thread.java:1019)
04-23 21:55:01.449: ERROR/AndroidRuntime(415): Caused by: java.lang.NullPointerException
04-23 21:55:01.449: ERROR/AndroidRuntime(415):     at com.locationReminder.viewPOI$LoadAllPOI.doInBackground(viewPOI.java:96)
04-23 21:55:01.449: ERROR/AndroidRuntime(415):     at com.locationReminder.viewPOI$LoadAllPOI.doInBackground(viewPOI.java:1)
04-23 21:55:01.449: ERROR/AndroidRuntime(415):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
04-23 21:55:01.449: ERROR/AndroidRuntime(415):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
04-23 21:55:01.449: ERROR/AndroidRuntime(415):     ... 4 more

This is the php code

$_POST['lat'] = 112;
$_POST['lng'] = -70;
$lat = $_POST['lat'];
$lng = $_POST['lng'];
$konteks = $_POST['konteks'];
$data = array();
$hasilHitung = array();
if (isset($_POST['lat']) && isset ($_POST['lng']) && isset ($_POST['konteks'])) {
$result = mysql_query("select * from poi where konteks_lokasi = '".$_POST['konteks']."'") or die(mysql_error());
if(mysql_num_rows($result) > 0){
    while($row = mysql_fetch_assoc($result)) {
        array_push($data, array('latitude' => $row['latitude'], 'longitude' => $row['longitude'], 'nama_lokasi' => $row['nama_lokasi'], 'konteks_lokasi' => $row['konteks_lokasi']));
    }
} else {
    $response["success"] = 0;
    $response["message"] = "Tidak ada lokasi berkaitan";
    echo json_encode($response);
}

for($i=0; $i<count($data); $i++) {
    $hasil = calDistance($lat, $lng, $data[$i]);
    floor($hasil);
    $hasilHitung[$i] = $hasil;
}

asort($hasilHitung);
print_r($hasilHitung);

for($a=0; $a<count($hasilHitung); $a++) {
    $response["point"] = array();
    array_push($response["point"], $data);
}
$response["success"] = 1;
echo json_encode($response);
}

function calDistance($lt, $ln, $data) {
$distance = sqrt(pow(($data['latitude'] - $lt), 2) + pow(($data['longitude'] - $ln), 2));
return $distance;}

And the java code

    class LoadAllPOI extends AsyncTask<String, String, String> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        progress = new ProgressDialog(viewPOI.this);
        progress.setMessage("Mengambil data...");
        progress.setIndeterminate(false);
        progress.setCancelable(false);
        progress.show();
    }

    @Override
    protected String doInBackground(String... args) {
        // TODO Auto-generated method stub
        //mendapatkan data dari database berupa alamat, konteks, latitude, longitude
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        params.add(new BasicNameValuePair("lat", Integer.toString(latPengguna)));
        params.add(new BasicNameValuePair("lng", Integer.toString(lngPengguna)));
        params.add(new BasicNameValuePair("konteks", konteksCocok));
        JSONObject json = jParser.makeHttpRequest(url_webservice, "POST", params);
        Log.d("data: ", json.toString());

        try {
            int sukses = json.getInt(TAG_SUCCESS);
            if(sukses == 1) {
                POI = json.getJSONArray(TAG_POIN);
                for(int i = 0; i < POI.length(); i++) {
                    JSONObject c = POI.getJSONObject(i);
                    int latDB = c.getInt(TAG_LAT);
                    int lngDB = c.getInt(TAG_LNG);
                    String alamat = c.getString(TAG_ALAMAT);
                    String konteks = c.getString(TAG_KONTEKS);

                    //buat fungsi k-NN setelah mendapatkan data dari database dengan parameter latitude, longitude, konteks
                    Log.d("latPengguna", "data: " + latPengguna);
                    Log.d("lngPengguna", "data: " + lngPengguna);
                    Log.d("latDB", "data: " + latDB);
                    Log.d("lngDB", "data: " + lngDB);

                    HashMap<String, String> map = new HashMap<String, String>();
                    map.put(TAG_ALAMAT, alamat);
                    map.put(TAG_KONTEKS, konteks);
                    POIList.add(map);
                }
            } else {
                Log.d("JSON error", "JSON trouble");
            }
        } catch(JSONException ex) {
            ex.printStackTrace();
        }
        return null;
    }

    protected void onPostExecute(String file_url) {
        progress.dismiss();
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                // TODO Auto-generated method stub
                //menampilkan data ke listView
                ListAdapter adapter = new SimpleAdapter(viewPOI.this, POIList, 
                        R.layout.list_item, new String[]{TAG_ALAMAT, TAG_KONTEKS}, 
                        new int[]{R.id.alamatPOI, R.id.konteksPOI});
                setListAdapter(adapter);
            }

        });
    }

The JSONPArser class

public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";

public JSONParser() {

}
public JSONObject makeHttpRequest(String url, String method, List<NameValuePair> params) {
    try {
        if(method == "POST"){
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);
            httpPost.setEntity(new UrlEncodedFormEntity(params));

            HttpResponse httpResponse = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();

        }else if(method == "GET"){
            DefaultHttpClient httpClient = new DefaultHttpClient();
            String paramString = URLEncodedUtils.format(params, "utf-8");
            url += "?" + paramString;
            HttpGet httpGet = new HttpGet(url);

            HttpResponse httpResponse = httpClient.execute(httpGet);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();
        }          

    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(is, "iso-8859-1"), 8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        json = sb.toString();
    } catch (Exception e) {
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }

    try {
        jObj = new JSONObject(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }
    return jObj; 
}

}

The json data response

   {
    "point": [
        [
            {
                "latitude": "112",
                "longitude": "75",
                "nama_lokasi": "ITS",
                "konteks_lokasi": "kuliah"
            },
            {
                "latitude": "145",
                "longitude": "-80",
                "nama_lokasi": "Teknik Kimia",
                "konteks_lokasi": "kuliah"
            }
        ]
    ],
    "success": 1
}

i'm so glad if you could help me... Thanks