The built-in "unzipper" in Windows doesn't like it, and neither does my rather old version of WinRAR. Looks like it's time to upgrade to the latest version of WinRAR - it can (according to the website) handle ".7z" archives, as fjtorres confirms.
Could you try to persuade PB to re-upload them as ZIP files? It would make life a LOT easier for people
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