I'm trying to get coop to work with some friends, but at least Direct IP doesn't work for all of them. Which is okay, because there are ways around that.

However, one of my friends is running into the following problem: when they click on "Join game", they get the dreaded "Invalid CD key". I've read a lot of comments by people who get that when they try to host a game, but what can you do if you get it when trying to join?

(It gets even weirder: the same guy was able to click on "Join game" last Saturday, but he was unable to connect. The connection just timed out.)