Unknown UdpMsg typeError

I cannot play a match with anyone else for some reason now.

[Assertion: FALSE && "Unknown UdpMsg type." @ ..\source\network\udp_proto.cpp:287]

This error keeps coming up after we've selected our characters and crashes the game. I have the latest Fightcade (42.2), all of my games load fine offline, I have my router forwarding 6000-6009 UDP and 7000 TCP.

Anyone seen this error before?