Getting Disconnected on Mario Kart Wii Wiimmfi Race: Why?

Sometimes when I do online races on Mario Kart Wii I get disconnected. It happens mostly at the end of a race. Sometimes it happens just before the race, and sometimes in the middle of the race! It says 'You have been disconnected from the other players'. Then it takes me to the Mario Kart Wii Main Menu or to the Wiimmfi Menu. Then I just race again until I get disconnected again. Why does it do that and what is the reason for it?

Here is how it went yesterday.

I was first place. I was like
Then the game screen turned black. I was like
Then it said I was disconnecte. I was like and and !

I was screaming loudly and smacking the ground!.. well maybe I was exaggerating a little...