Build 3.5.0.44 of xlsgen improves how malformed XLSX files are read. Third party components generating XLSX files may use a non-standard XLSX file format (ZIP and other), which in turn causes problems for Excel or xlsgen to open.

xlsgen takes care of this particular form of malformed XLSX file (uses PKWARE data sections). And should there be another one, which xlsgen can't handle as is, a special error code is returned (0x80072004) which lets a client application know there is a problem with the file format itself.