Sounds to me like you’re either missing a file or two, one/multiple ones are corrupted or incomplete downloads, or you’re somehow performing the unpacking process incorrectly.
What programs have you tried using, and what’s the process you used with these programs?
-WinRAR for Mac
I tried to follow the instructions as closely as I could, extracting Part 1, but with The UnArchiver and Dr. UnArchiver, I always got an error on Part 6. WinRAR for Mac wouldn’t open. As for iZip, it did, indeed, work, but the problem with iZip was that I didn’t know how to move the finished file to my hard drive.