I recently bought Neverwinter Nights 1 for me and my friend and we both got the multiplayer keys.

But I can't join his games and he can't join me, but I can join other people's games.


Help please. D:

Could be a firewall issue.
If you're using a router, you could need to do some port forwarding. Here you can find a detailed guide for many routers.

Anyway, here is the list of ports that must be opened, according to game's readme:

Outgoing packets:
Source port: 5120-5129
Destination port: 5121-5300

Incoming packets:
Source port: 5121-5300
Destination port: 5120-5129
Protocol: TCP/UDP