Hey I just wanted to thank you for something you posted back in 2011. I was having problems getting online the Wifi Plaza in HeartGold on my new DSi XL (from ebay), so I googled "pokemon heartgold dsi wifi plaza error 51099 wpa2" and a whole 2 pages of results came up... yeah :/
Anyway among them was a post from you, which if I hadn't come across would have left me stressing out over my newly purchased DSi...
The only thing you can do is get a DSi and higher liket the XL and 3DS as they support WPA but here is the catch. Diamond Pearl Platinum Heart Gold and Soul Silver do not work on WPA and the only games that do work on WPA are Black and White. If you are thinking of getting a DSi get Black and white then transfer all your data to Black and White.
... So I signed up just to personally thank you... seriously I needed to haha! All the best!