Blue Screens with Multicore in Counter Strike Source

I've played Counter Strike Source using the multicore option previously with no problem. Now after on average 20 or 30 minutes of play I get a blue screen with the following error message:

Code:

A clock interrupt was not received by a secondary processor

I've even started with a clean Windows install with the latest Nvidia drivers and have had the same problem. I've tried previous driver versions, I've tried adjusting the voltage to my CPU and northbridge even though they are normal, I've tried reseating everything in the computer, I've swapped in another power supply, I've disabled my antivirus program, I've disabled the steam overlay, temps are fine, I've tested my ram and hard drive, updated my bios and cleared the cmos, and none of it has helped. I only get this blue screen with CSS, I can't reproduce it with any other game. Strangely it seems to happen most often in a particular part of the office map. I do not get the problem without multicore disabled, but I would still like to get to the root of the problem.

Thanks in advance.

For what it's worth I think SP1 solved this problem