Things like this do happen during updates.
Can you do a file verification for GG please and see if it will recue for you the missing files.
This should take care of it, plus a restart steam and GameGuru, has helped this also.
Let me know if you are still having issues, as we thought this had been solved already. Thanks
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