Sorry for the delay in response.
Tried multi player on a very basic map with just 4 start markers.
I received the same error as you.
I will have to look into this more.
Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz, 2400 Mhz, 4 Core(s), 4 Logical Processor(s), 8gb RAM, Nvidia gtx660, Windows 7 Pro 64bit, Screen resolution 1680 x 1050.