I was having the same problem. After some diagnosis, it turned out that the file is compressed using a new, paid version of WinRAR (likely 5.8+). It can be unpacked using the newest evaluation version downloadable from WinRAR's official website.
That said, I do urge the author to use common versions of WinRAR (e.g. 3.9) to compress the game files. The new versions of WinRAR provide no useful functions other than coercing the users to pay for new "features."
GameTheory_Nod25
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