Technical issues with Heroes III.

For a cleaner experiment, try not just disabling the antivirus, but uninstalling it! Then reinstall it. As for the firewall, disable it in the services – stop it and set it to "Disabled." If we're talking about the built-in Windows firewall, or uninstall it if it's Comodo, Agnitum, etc.

Just recently, a friend and I wanted to play, but couldn't because he installed Norton Security, and even after "disabling" it, it didn't help until he completely uninstalled it.