Could be 2 things:
1. Check to make sure your modem and/or router has a connection from your ISP and if your Wii is properly connected to the internet.
2. Check to make sure the SD card isn't write protected. Sometimes when I insert my SD card into my Wii the slider gets set to the "lock" position, preventing data to be written to the card. I have had problems with the HBB when my SD card is locked. (complains about the repository not being found and goes into an endless loop)