Instead, place it next to the installer, but only if you trust the source (e.g., extracted from an official Inno Setup installation).
Use System Restore (if the error started recently): isdone.dll download windows 7 64 bit
If you are trying to install a large game or software suite on Windows 7 and are met with the error message or "Unarc.dll returned an error code -1/5/6/7," you are not alone. This is a notoriously common issue for users running older operating systems or attempting to install repacked games. Instead, place it next to the installer, but