Three things you should probably try are to make sure your Wii is on the latest firmware, make sure your are connected to wifi, and try retyping in your MAC Address into letterbomb.
Two of the three things are working the third one I can't test right now because my brother is using the internet cable and it won't work wirelessly. I will ask him if I can use it. thanks for the help!
Very much this. If the Wii system date is wrong, the letterbomb won't show up at all. Also even if the date is set correctly, you may have to go forward or backward a day or two due to timezones.