There are two reasons to do this: Either your computer is not attached to the internet. Or you have a computer that can not resolve to the Rhino validation server because of firewall or other blocking program or configuration.
To test access to the validation server, use this link. You should see a page that the site is not for humans. If you can't reach that page, you are blocked, probably by a local firewall.
Rhino licenses must be validated before they can be used. For offline computers, you can perform license validation offline.
Rhino will now be successfully validated offline.
Note: For network-wide deployment and using an offline LAN Zoo, the necessary data is presented when you try to add a license to that Zoo. For a Zoo-specific write-up of the preceding instructions, see https://wiki.mcneel.com/zoo/rhinovalidateoffline#validating_offline