I use Chilkat ZIP on VC++ for a software application that's run for years.
Suddenly, some users are reporting that the ZIP file isn't being written at all on their computers. On other computers (like mine), it's fine. I'm guessing (!) it has to do with a Microsoft Windows 10 update or a Microsoft support library changing or being missing.
Have you checked the permissions - AD/local accounts. Normally not allowing you to write.
Duh, I am fighting the same kind of problem, runs fine on a 2k3 server, but simple will not work on a windows 12 server. Failure is totally random. WindowsError: The specified network name is no longer available.
Are you sure you are checking the return code on all chilkat calls?