This usually happens if part2 was not downloaded completely or got corrupted. Try re-hashing the torrent or re-downloading part2 .
Use the latest version of WinRAR or 7-Zip to extract only part1 . It will automatically pull data from part2 and the rest. Common Errors: Ground [FitGirl].part2.rar
If you are currently looking at or dealing with this file, here is the necessary context and troubleshooting steps: This usually happens if part2 was not downloaded