"Unsupported encryption" + unarc.dll error code 11 usually means one of two things: either the unpacker that you are using does not support the compression/encryption method used by the archive, or the archive is damaged/corrupt. As perhaps you already tried re-downloading, run as admin and turned off antivirus I will advise you to try another extractor or version. install latest 7-Zip and Latest WinRAR I (unrar) and try again with the following tools. Also WinRAR has a "Test archive" feature which does tell you if parts have CRC errors. If it's an SFX installer, an outdated deleted game, or a re-pack that is utilizing a very particular kind of unpacker, the incorrect tool will show the unsupported encryption message even though the file might in fact be okay.