This means one of the parts downloaded with a corruption. You will need to delete that specific part and redownload it.

Ensure you have downloaded happy_mining.part1.rar , happy_mining.part2.rar , and any subsequent numbered parts.

Right-click on ( happy_mining.part1.rar ). Select "Extract Here" or "Extract to happy_mining/" .

Move all files into the exact same folder on your computer.