Plutonium

I can't enable uPnP for some reason, so I made my friend create a custom game that I decided to join. But, when I double click on his name after his status says "playing a private match" it just shows me a loading dialogue which says "joining game session" and then it disappears without letting me into the session. I thought this was because his game's privacy was closed, but even after setting it to public I couldn't join. We also tried removing all the bots before starting the game, but that couldn't help either