Error #1069: Property Pertanyaan0 not found on String and there is no default value - flash-cs5

Question

I stuck here please help, i'm new in flash, using adobe flash cs5.5
Here's the code :
import flash.net.URLLoaderDataFormat;
import flash.events.DataEvent;
stop();
alert_mc.visible = false;
alert_mc.ok_btn.visible = false;
var score:Number = 0;
var jawaban;
var nextQst:Number = 0;
var i:Number = 0;
a_btn.addEventListener(MouseEvent.CLICK,btna);
function btna(ev:MouseEvent):void
{
cekJawaban("a");
}
b_btn.addEventListener(MouseEvent.CLICK,btnb);
function btnb(ev:MouseEvent):void
{
cekJawaban("b");
}
c_btn.addEventListener(MouseEvent.CLICK,btnc);
function btnc(ev:MouseEvent):void
{
cekJawaban("c");
}
d_btn.addEventListener(MouseEvent.CLICK,btnd);
function btnd(ev:MouseEvent):void
{
cekJawaban("d");
}
var qvar_lv:URLLoader = new URLLoader();
qvar_lv.dataFormat = URLLoaderDataFormat.TEXT;// Step 1
qvar_lv.load(new URLRequest("DaftarSoal.txt")); // Step 2
qvar_lv.addEventListener(Event.COMPLETE, onComplete); // Step 3
function onComplete (event:Event):void // Step 4
{
var faq:String = event.target.data; // Step 5
trace("Success"+faq);
if (faq["Pertanyaan"+i] != undefined) {
no_txt.text = "PERTANYAAN KE-"+i;
soal_txt.text = faq["Pertanyaan"+i]; ja_txt.text = faq["a"+i];
jb_txt.text = faq["b"+i];
jc_txt.text = faq["c"+i];
jd_txt.text = faq["d"+i];
jawaban =faq["benar"+i];
} else {
gotoAndStop(3);
skor_txt.text = score+"";
teks_txt.text = "Score akhir kamu :";
}
}
function cekJawaban(val) {
alert_mc.visible = true;
if (val != jawaban) {
alert_mc.alert_txt.text = "jawaban kamu salah, score anda berkurang 50 points";
score = score-50;
alert_mc.ok_btn.addEventListener(MouseEvent.CLICK,btnok);
function btnok(ev:MouseEvent):void
{
nextQst = i+1;
alert_mc.visible = false;
}
} else {
score = score+100;
alert_mc.alert_txt.text = "jawaban kamu benar, score anda bertambah 100 points";
alert_mc.ok_btn.addEventListener(MouseEvent.CLICK,btnok2);
function btnok2(ev:MouseEvent):void
{
nextQst = i+1;
alert_mc.visible = false;
}
trace(score);
}
}
Error #1069:
Property Pertanyaan0 not found on String and there is no default value.
at revisi_fla::Symbol5_68/onComplete()
at flash.events::EventDispatcher/dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at flash.net::URLLoader/onComplete()