Is the machine on a different Subnet than the Keyserver? If so, you need to explicitly tell it where the server is, as the auto search will only search within the current subnet.
To tell the machine where the server is, open up the webadmin (
http://localhost:22350 in your browser) and go to the Configuration tab.
Now you can add the server to your Server Search List by clicking the Add button. Enter the IP address or name of the server and then click OK (I usually add the name first, and then hit Add again and enter the IP address as well).
Make sure you hit the 'Apply' button to save your changes, and then try firing up ARCHICAD again.
Josh Osborne - Central Innovation
HP Zbook Studio G4 - Windows 10 Pro, Intel i7 7820HQ, 32Gb RAM, Quadro M1200