Read the FAQ on 7zip site.
"Why can't 7-Zip open some ZIP archives?
In 99% of these cases it means that the archive contains incorrect headers. Other ZIP programs can open some archives with incorrect headers, since these programs just ignore errors.
If you have such archive, please don't call the 7-Zip developers about it. Instead try to find the program that was used to create the archive and inform the developers of that program that their software is not ZIP-compatible.
There are also some ZIP archives that were encoded with methods unsupported by 7-Zip, for example, WAVPack (WinZip)."
Also if a .7z archive from a forum, torrent DC+ share etc might be using a derivitive fork of the common compression method that regular stock 7 zip can't recognise.
Crack Teams, modders etc will often do this to make it unreadable by unorthorised people without having to bother with passwords and acts as a pseudo-encryption.
On the more likely scenario the archive is corrupted.
· 5 years ago