When you click on the letter? You mean letterbomb? That's not launched from the homebrew channel... so gonna need u to describe the issue better, no one will be able to help u with that kind of report
Scratch that I can help. Resoftmod your wii as if it were a virgin even if it isn't using using modmii. If u encounter an issue with the hackmii installer, run the modmii hackmii solutions wizard (this is also stated in the main Modmii Wizard/guide).
Do that and your issue should be resolved without me even knowing what the issue is.