Problem with SketchUp Pro 2018 Installation

[Anssi]

Explanation and instructions in this thread:

2018 Pro keeps telling me I am not online.!

I just installed 2018 on my computer (as an administrator), but cannot register the software because 2018 says I am offline. My computer is hardwired to our network. I have re-installed it several times, and the same thing happens. I even contacted IT about a possible firewall conflict, but no resolution. Any suggestions?