Make sure that you have a Nintendo DS Game Card properly inserted into the Game Card slot of the system (how to come here:http://www.nintendo.com/consumer/systems/dsi/en_na/gameCards.jsp). If you have made sure the game is being inserted properly but are still getting this message, then your system will need to be repaired. Please ( click here http://www.nintendo.com/consumer/repair/dsi_repair_home.jsp?problem=TWRECGAME )for repair options.
Important Note: If you only have one game that is experiencing this issue, it is likely a problem with the Game Card and not the system. Please ( click here http://www.nintendo.com/consumer/systems/dsi/en_na/replace_game.jsp)for individual Game Card repair and replacement information.