If instead of zip files you find a message saying "Cannot open file: it does not appear to be a valid archive", it means that the files are damaged and stand in need of zip repair. To fix the problem, open the files in Zip Repair Tool. The program features a sophisticated recovery algorithm that restores zip structure integrity and helps recover zip files with their contents. You can easily repair zip files of any size and number of volumes.

Version 3.1 added the "Do not create repaired Zip file, just extract files from damaged Zip archive" option.