ARMA 2 Connecting failed (friend's server)

[helckler 10]

So, I and my friend both live in the same city and we used to play ArmA 2 campaign together and join each other armory. We used to do it without any problems. We'd just host the server (either campaign or armory one) and we'd join it to have tons of fun. But I then had to reinstall steam because I formatted my computer. Since I reinstalled windows and steam, every time I try to join his servers it shows up a "Connecting Failed" message and vice-versa. I wonder what can we do to play in each other's servers like old times.

Thank you.