Hi Anton,
"0" is not a valid HTTP response code, so it is not being sent from our corporate server. You are getting a status code of 0 because the connection request is timing out, that is, there is no connection established between your computer and our server after a reasonable waiting time. This problem can be caused by multiple factors, but it is related to a problem with Internet connections on your machine, not in PixInsight. It's very true that misconfigured firewalls typically cause these problems on all platforms.