ANDROID / Error parsing a JSON object encoded string

my code receives a JSON object coded string from the server, which can be: [{"logstatus":"0"}] or [{"logstatus":"1"}]

Then it converts this JSON (received as ImputStream), then I convert it to a string and later I want to convert it to a JSON object. But here it appears an error. Here is my code:

public JSONArray getserverdata(ArrayList<NameValuePair> parameters, String urlwebserver ) {   
  httppostconnect(parameters,urlwebserver);    
  if (is!=null) { //si obtuvo una respuesta    
    getpostresponse();    
    return getjsonarray();   
  } else {   
    return null;    
  }
}

private void httppostconnect(ArrayList<NameValuePair> parametros, String urlwebserver) {
  try {
    HttpClient httpclient = new DefaultHttpClient();
    HttpPost httppost = new HttpPost(urlwebserver);
    httppost.setEntity(new UrlEncodedFormEntity(parametros));
    //ejecuto peticion enviando datos por POST
    HttpResponse response = httpclient.execute(httppost);
    HttpEntity entity = response.getEntity();
    is = entity.getContent();
  } catch(Exception e) {
    Log.e("log_tag", "Error in http connection "+e.toString());
  }     
}

public void getpostresponse() {       
  try {    
    BufferedReader reader = new BufferedReader(new InputStreamReader(is,"UTF-8"),8);
    StringBuilder sb = new StringBuilder();
    String line = null;
    while ((line = reader.readLine()) != null) {
      sb.append(line + "\n");
    }
    is.close();
    result = sb.toString();
    Log.e("getpostresponse"," result="+sb.toString());
  } catch(Exception e) {
    Log.e("log_tag", "Error converting result "+e.toString()); 
  }
}

public JSONArray getjsonarray() {
  //parse json data
  try {       
    JSONArray jArray = new JSONArray(result);
    return jArray;
  } catch(JSONException e) {
    Log.e("log_tag", "Error parsing data "+e.toString());
    return null;
  } 
}

The error is in the function getjsonarray().

Error parsing data org.json.JSONException: Value ?? of type java.lang.String cannot be converted to JSONArray.

I have verified that the server returns a JSON with good format (which can be [{"logstatus":"0"}] or [{"logstatus":"1"}].

Also I've tried to use JSONToken but it doesnt work either.

Hope you can help me!