Possible solution:

1. GT lite Game launcher

2. > Server Setup

3. > Add server

4. > Add Game: Arma 2 Operation ArrowHead Retail(Make in Game Setup>Add Game> Retail.

5. > Fill in chosen server ip from Game Tracker homepage.

6. > Apply and ok. Important to do both.

7. > Start game through GT Lite Launcher.

8. > Get in the fight!

Had a lot of trouble getting it to work since the steam version. And I also kept using arma 2 original when adding game through game setup and server setup. Since Game Tracker launches the original game. I hope this works for you all and see you ingame