Hmmmmmmmmmmm... did you install the software first? And did ya run the software then turn the Wii on? I think I got this error at first, I think XD Make sure the Nintendo WiFi Software is open also and that you've allowed access.
I dunno what you ave or have not tried, so try some of these things:
Go to the Wii Control Panel
Find the "Internet" button
Click on "Connection"
Click "Use this Connection" (it may/should say Nintendo WiFi)
Then click "Connection Test"
You may even try "Clear settings" then repeat the above options.