The ZBrush Trial requires internet access every time it is launched. There is no way to bypass this. If your computer cannot be connected to the internet, you will not be able to use the Trial. You will be able to use a purchased license, however -- only the Trial requires internet access.
If your computer has internet access but the Trial tells you that it can't connect, the most likely cause is a firewall installed on your machine.
In many cases, a prompt will appear asking for permission to access the internet. If your firewall gives such a prompt, please say yes.
If this doesn't happen then you will need to open the firewall for ZBrush. There are two things to check/try:
- Go to your firewall's settings and add ZBrush as an allowed program.
- Make sure that register.pixologic.com is whitelisted as an allowed web address.
- The Trial uses ports 80 and 443 to communicate with this address. As they are the default web browser ports, there most likely will be no need to add special permissions for those ports.