Note that the update in question is not a 'Security' update, it's just a normal update, in the list the exact name should be 'Update for Microsoft Windows (KB2670838)', not the 'Security' ones. I have been able to play Clear Sky without crashes since then. I then rebooted the computer, it did some changes and then got back to the desktop normally (it's just one update you manually remove anyway, nothing important). From that list I scrolled down and found the update in the list and uninstalled it. I found the update in question in Control Panel > Programs > Programs and Features > Installed Updates. So I looked around with Google, searched some forums and eventually stumbled upon that, the 'KB2670838' update is supposedly known to cause crashing with Clear Sky. I was having crashes in Clear Sky left and right, even though my system isn't over-clocked (maybe yours is, however, is it? If it is maybe it's related to an over-clock instability, who knows) and none of my games crash (haven't had a game crashing on me in months). It's going to sound strange (I thought it was, too, when I first read about it) but I fixed my Clear Sky crashes (with and without mods, including Clear Sky Complete) by uninstalling a very specific Microsoft Update, namely 'Update for Microsoft Windows KB2670838'.

Stalker clear sky complete