Thanks. No NAS volumes here. But internet access was, of course, the issue for second case. Proxy setting doesn't work for this update downloader? Gave the host full internet access and all fine - downloads the update, ready to be accepted.
But still can't do the local upload (which I don't need now anyway).
If you are running a very old build of DSSv6 and you want to update to the latest, try to update to build in between first before you reach the last one.