The game is now sold on modern platforms like Steam, where the DRM is handled differently (or not at all, depending on the title). The old Reflexive "wrapper" has been stripped away.
The safest and most reliable way to play Chicken Invaders 3: Revenge of the Yolk is through modern storefronts. The developer, Interaction Studios, still maintains the game. Official Website: You can purchase the full version directly from Interaction Studios chicken invaders 3 activation code reflexive