mmmm, silly question: are you trying to decompress it by its own, or together with part 1?
They are not separate RAR files, they are ONE file splitted in two, and thus they must be decompressed together, just put them in the same folder and go to decompress the first part, they will be both unpacked.
Meanwhile, I'm trying to see if there are any other troubles! I'm downloading again the files to see if they are corrupted, if it's so I'll tell you and solve the problem.
Not so silly at all it turns out

My computer should have known this before admonishing me when I tried to extract part 2. Sometimes I think it throws error messages around just to hear itself beep.