This is indeed a mystery! I downloaded and ran the same install package on my Win 8 system, and found the 7z folder and setup.exe within. It's as if it's failing to self extract on your machine for some reason? Never heard of that before but anything is possible i guess. Again I would counsel trying 3rd party ZIP software (WinZIP, WinRAR, etc) and extract the package manually, and then find setup.exe and try again.
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