cant join a friends game/ failed to join game

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JuBge
Fallen
1 | 0
Greetings,

if my friend creates a ladder game and i try to join, i always get "failed to join game".
if i open a game he can join without a problem and we can play together.
we always go with a simple name + passwort

i tryed to google it and search the forum directly but i didnt found something.
ports shouldnt be an issue or ? we opend UDP/TCP 4000 and 6112

and if u want to kow why i doesnt host then all the time, it is because i want to help his 2nd char to get faster to hell =)