WPA or WPA2 will not work for old DS games. Only games that are DSi-enhanced and all 3DS games can use them. If you switch to WEP security (Which isn't the best idea), you can use your old games. But if you do decide to use WEP, the 3 main setups won't work, rather, you must configure them separately:
1. Go to System Settings from your Home Menu, and tap Internet Settings. Enter your pin if prompted.
2. Tap Nintendo DS Connections (Third option), then tap Yes on the subsequent popup.
3. From here, tap Nintendo Wi-Fi Connection Settings, then pick a connection. You should know the rest.
