Did you paint grass on the terrain with the grass brush in the editor or in F9 mode in test game?
Is this a custom one you may have created?
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