Technical issues with Heroes III.

I downloaded the build. I installed it, the local network is configured, meaning there is ping and the computers can see each other (access is open), the game launches and everything works, but when connecting via TCP/IP, one computer cannot see the other that is acting as the server, and vice versa. What can be done, and what could be the cause? Thank you! Maybe some additional files need to be installed? Help me solve this issue! One computer has Windows XP, and the laptop has Windows 7. Before this, I tried it and played with a friend.