A large archive created by a parallel version of GZip is periodically supplied by an outside organisation. This archive has an GZip member at the begininning that contains only a file comment with no compressed data which is followed by a member containg the compressed data. Version 4.65 of 7-Zip and version 1.3 of GnuWin32 Gzip both successfully decompress this file but versions 9.20 and 9.25 Alpha of 7-Zip report “Cannot open file as archive”. If the initial GZip member is removed from the archive version 9.20 recognises it as a GZip archive and processes it. Ideally we would like to use the latest version of 7-Zip but at present this is not possible.