802.11b - Most routers are backwards compatible with the 802.11b standard. Routers that broadcast exclusively on 802.11g or 802.11n may not be compatible with the Nintendo DS nor the Wii.
WEP - If you wish to secure your wireless network, the Nintendo DS and Nintendo DS Lite are only compatible with WEP (Wired Encryption Protocol).
I think that bold part is your problem. =3 Yes, I know it works on your Wii, but It sometimes happens. O_o