In the most 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 7zip 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 7zip, for example, WAVPack (WinZip).