Error while unzipping Wii games

Hi,
I want to download just some Wii games for Homebrew and I cannot manage. Every game I downloaded has an error when it comes to unzipping. It doesnt matter what
format (7z or zip),
program (Linux Archive manager, online unzippers or 7z on Windows) or
Software site (Vimms Lair and some other site from given FFA links)
is used, I always get the same error:
- The archive manager sees the files (.wbfs and .txt) inside
- archive manager starts unpacking
- archive manager stops with undefined error and returns a much too small (some MB) file.

For Vimms Lair, I had the problems with TLOZ Skyward Sword and Sonic Colors.
Does anybody has a clue what I am missing?