If the installer itself is corrupted but the raw archive is fine, you can bypass the problematic unarc.dll entirely.
Error code 6 specifically can sometimes mean "Read Error." This happens if your RAM is faulty or your hard drive is full. how to fix unarc dll returned an error code 6 fifa 13 link
The typically occurs during the installation of highly compressed game repacks (like If the installer itself is corrupted but the