It is not a ZIP file, it has no extension, but be careful that if you handle it with a Mac, or with a software that recognize ZIP from the compression markers and not from the extension, it can happen that your system sees it as a ZIP, but I don't know how to solve it because I don't know Mac, or the softwares. This happens with every board file for VASL. We fully tested them.
Hi - thanks for getting back to me - yes, it appears that chrome was deciding it was a zip file for me, and saving it as such. Strange - when I download it using curl (to avoid the file being messed with in chrome) and try to load it in VASL (6.5.0), I get:
020-07-17 17:33:00,440 [1-AWT-EventQueue-0] WARN VASSAL.tools.ErrorDialog - Unable to open board file: bdSollum
2020-07-17 17:33:00,443 [1-AWT-EventQueue-0] ERROR VASSAL.tools.ErrorDialog -
java.util.zip.ZipException: invalid END header (bad central directory offset)