The problem with the keycards used on the the mk2 Megane and Laguna models is the lack of rigidity of the cards. They could bend quite easily, causing stress on the inner parts and cracking the solder joints on components.
If when pressing the buttons on your keycard you cannot get the car to unlock, you most likely have either an defective button, or a broken solder joint on the transmitter coil inside the card. Opening the card is quite a task, but is worth a shot, with the price of a new card from a Renault dealership in Ireland being between €240-300.
The video below shows how to open the card and re-solder the transmitter coil.