There are just a handful of common reasons why people can’t join your Listchecker games. LC does a good job in telling you with its log that opens up along with the program. Obviously when it says “Game hosted with success”, you have no problems, but there will be times where it says “CD key in use” or “Failed to create game”. That error almost always has to do with someone else already using the game name. So changing that will definitely make it work.
However, LC won’t tell you that your Warcraft III port is blocked. Google a port scanner tool and have it scan your Warcraft port (default 6112). Also make sure that the LC config file has the same port that you forwarded. The game port that you set in-game have no bearing on the LC port. The only requirement is that it must be different than the LC port, but that port number is not important for hosting games.
The last issue is quite obscure. I ran into an issue where one of my friends couldn’t join my game, but everybody else could. Warcraft simply gave him a gray screen. I immediately thought that it was a problem on their end and not mine. However, upon closer inspection, it appears that if I set my LC hosting port to default, everybody can join. The reason I didn’t use the default port is because someone else was using the 6112 port and I couldn’t forward the same port on multiple computers. I don’t really know why that is, but it works beautifully.