Uh oh. I've gotten this "not a valid archive" error after downloading three times in a row.
The first archive you downloaded would have worked properly. It's a 7 zip archive, created using zip compression, and has a .zip extension. The issue you are having is because you're trying to open it from the FOLDER pane
, but it is not a compressed folder. So rather than trying to open the folder, click on the archive file itself in the FILE PANE.
Do that and it will open like normal.
i.e. the operating system likes to treat .zip files as extended compressed folders, but instead it's finding a 7-zip structure, but nevertheless the archive is fully functional for its intended purpose, to deliver an extractable mod to the user, in a compressed format, that can be opened by any unzipping utility.