Help! We're having the following issue: we're trying to play together using Hamachi, the chat works, but we can't ping each other's computers. In the game, if I'm the server, the other person can't see me; if they're the server, I can see them, but when I try to join their game, after a 20-second pause, I get a message saying something like "a connection error occurred." We have the same versions of the game and Hamachi, and the program has been added to the firewall as described above.
Does anyone know what to do?

P.S.: We had no problems playing with another person...