[help] Cannot boot server.

Hi, since last update I cannot start a multiplayer server from inside the main game. The only way to achieve a multiplayer server is to use the dedicated server, but it takes two to three tries until it "catches" and people can get in.
When I try to start a server using the main game, it says "Cannot boot server." just before "<name> entered game" in the chat box.
What does this mean?

I'm running Win8.1 x64, starting game and dedi server as admin.
Ports opened in firewall and forwarded in router are 34747 TCP, 34597 and 34697 UDP.
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