I'm trying to load my lan game of NWN core campaign, but when I click the save file, it pops up the message "Cannot translate address"

It's been a few months since I played it, but I used to have no trouble hosting this on my lan. What have I done wrong to break it?

The error message you received is odd, since it strikes me as a DNS error. So to clarify, this occurs when you load a save game created from a hosted multiplayer game, yes? If this is the case, was the server using the dedicated server tool to host?