Interfacing arduino with LabVIEW

Question

I have already downloaded the arduino package for LabVIEW, MakerHub LINX, NI-Visa, and I've uploaded LIFA_Base to arduino, and it still does not work :(. My questions are:

1) Do I need to upload the LIFA_Base to arduino every time I want to interface arduino with LabVIEW, or is once enough? (the order I'm following is: upload LIFA_Base -> upload my arduino code -> run the LabVIEW code)

2) I know my arduino UNO is receiving info by the LabVIEW software because the RX led goes on every time I press the ON/OFF buttons, what could be the problem?

The ideia of this humble project is to turn on/off LED through the LabVIEW. The arduino code follows the LebVIEW code.

String c, string;
int led = 2;

void setup() {
   Serial.begin(9600);
}

void loop() {
   if (Serial.available() > 0) string = "";

   while(Serial.available() > 0)
   {
     c = (byte)Serial.read();
       if (c == ":")
       {
         break;
       }else
       {
         string += c;
       }
     delay(1);
   }

   if (string == "LL")
   {
     digitalWrite(led, HIGH);
   }
   if (string == "DL")
   {
     digitalWrite(led, LOW);
   } 
}