MP - cant play with Friends :(

[KarlJohnson]

3 Players - A, B and C

A and B live together, using the same Internet with their 2 PCs and their 2 steam accounts. C has own PC, INternet and Steam.

If A is hosting C can join, but B cant.
If B is hosting A can join, but C cant.
If C is hosting A can join, but B cant.

No useful error message. Just the line filling that the server doesnt answer.

[KarlJohnson]

B seems to be the problem - he cant join any public game.