From EA site:
"Okay, I've got a fix. The problem is caused by the router. I had use the DMZ setting on my router (demilitarized Zone) to give my wii unrestricted access to the internet, ie. completely exposed. This means that if someone figured out the correct ports to forward, you could also do that. Anyway, for now, pray you have a dmz option on your router, or go buy a new one.
Here's how I did it on my D-Link Router.
1. Go to router configuration probably 192.168.0.1
2. If you're not familiar with router configuration, you probably need to figure out your default password, you can do a google search for your router.
3. Configure your wii to have a static DHCP address (under DHCP)*
4. Go to Advanced, then DMZ and set your wii's static IP address as the Demilitarized Computer.
5. buy me a beer
*You can skip step 3, but you'll have to reconfigure the DMZ ip address everytime your router assigns your wii a new address.
Hope this helps as a temp. fix for most people until they tell us what ports to forward. "
I was with this problem, now I just configured my router to static dhcp for the wii and it's working..
gl