have the same problem and tried what NoQ said:
i typed in "ping lobby.wz2100.net" in my console and all packages get transferred => no problems.
another tip?
(i could successfully play online - even host games - till yesterday. i still have the 2100 udp/tcp ports open. firewall is also not the problem)
when hosting a game the game tells me that "failed to open a connection to port 2100". when i want to join the lobby it says "connection problem"

but the ports are fine. i could play till yesterday. and i rechecked the router settings. still everything correctly configured.
the only thing that happened yesterday: windows update. what could the windows update do so that my connection doesnt function anymore? i checked the ports. i reinstalled the game. i disabled firewall
