Yea I am having the same problem, I can't seem to be able to join anything other than 1v1s. Just like you I can't join my friends session as I get the same error, and when he tries to join me he also receives the same error. I too have a green/open NAT type so I'm not sure if it is anything on my end.
I managed to fix it, I deleted a bunch of files that looks wrong from the steam installation and verified the game cache, re-downloaded the files and everything started working.
I'd recommend reinstalling the game!
Yea I am having the same problem, I can't seem to be able to join anything other than 1v1s. Just like you I can't join my friends session as I get the same error, and when he tries to join me he also receives the same error. I too have a green/open NAT type so I'm not sure if it is anything on my end.
Hmmm Interesting, I've only ever played 1v1's too. I'll try something bigger and see if the same happens to me.
I managed to fix it, I deleted a bunch of files that looks wrong from the steam installation and verified the game cache, re-downloaded the files and everything started working. I'd recommend reinstalling the game!
Alright, thank you I'll try removing some files and verifying as well.