"unknow JoinEvent" (sic)

[Nemmy]

Hi!

I'm trying to play a co-op campaign, but each time I invite a friend to join me that friend gets the error message mentioned on the title. The same thing happens if my friend attempts to invite me.

Does anyone know any solutions to this issue?

[GrandMaster_JAX]

I had the same problem but it only happened because both of you need to update dawn of war 2.

[76561198139511516]

If you're running Dawn of War 2 and your friend is running Dawn of War 2 Chaos Rising, then you might get this error I think. Can't join coop or multiplayer across the two games. If you have both games, then just make sure you and your friend start the same game before trying to invite each other for coop.

[Foosball]

Remove " -dev from launch options" before booting the game fixed it for me.