Every time I try to host a multiplayer game Factorio crashes, saying that an unexpected error occurred. I can join other multiplayer sessions just fine, and singleplayer works.

Log

0.001 2016-09-02 09:33:42; Factorio 0.13.20 (build 24011, mac, steam)
0.001 Operating system: Mac OS X 10.8.5
0 ...