The standard zip format has changed a lot the last years. Some extensions have been added to handle Unicode file names, large files (zip 64), etc. Unfortunately not all archivers support them (or they support them partially). Cobian Backup creates zip files that are 100% compatible with the latest version of Winzip. The included decompressor should also handle these files without problems. Other archivers may or may not support all new extensions so you may get errors like "Archive corrupted" or "Unexpected end of the archive".