Wii connection help?

[#1]

Last night I tried to connect to a friends Wii for a game of Mario Karts, but it kept saying I was unable to connect. Also, trying connecting to the WFC was unseccessful.
The Wii does connect fine to the internet via my Wifi router as I can get weather and software updates.
I'm a complete novice with internet gaming, but could anyone give me any pointers to try and troubleshoot this, please?
Oh, and rule out that it's not my connection being overly throttled by Plusnet (I'm on "Your Way Option 2").
Cheers

[#2]

What are you settings on the broadband firewall? If it's on high it could be blocking the non-standard gaming ports.
Check here https://portal.plus.net/my.html?action=firewall

[#3]

It's on low.

[#4]

just done a quick search on this - it could be the Wii servers acting up rather than your connection