Nintendo Wi-Fi Connection match making service is undergoing temporary maintenance. This maintenance can prevent certain games from matching up opponents. I don't know how long this will last, but I got it from here:
http://www.nintendo.com/consumer/wfc/en_na/ds/results.jsp?error_code=84020&system=Wii&locale=en_US&action2.x=21&action2.y=18
http://www.nintendo.com/consumer/wfc/en_na/ds/results.jsp?error_code=84020&system=Wii&locale=en_US&action2.x=21&action2.y=18