From Mod Wiki
When STALKER crashes to desktop (CTD), it usually opens a bug-trap window that contains some error codes and log files. The window only opens, if you don't do anything after the crash, so you might want to wait a bit and see if the window pops up. The important information for debugging the error is stored in the log file. If you don't see the bug-trap window, you can still get the logged information.
A short log is also stored in your Windows clipboard. Open a text editor (Start - Run - type notepad - OK) and copy the log from the clipboard into the text editor (CTRL-V). You might as well copy it directly into a forum, where you ask for help. Short logs look like this:
Expression : 0 Function : CPostprocessAnimator::Process File : E:\stalker\sources\trunk\xr_3da\xrGame\PostprocessAnimator.cpp Line : 221 Description : noise.grain cant be zero! see postprocess Arguments : nightvision_bad.ppe
If more information is needed or the short log is no longer on the clipboard, you can open the log file on your hard-disk. It is usually located in:
English XP: C:\Documents and Settings\All Users\Documents\STALKER-SHOC\logs English Vista: C:\Users\Public\Documents\STALKER-SHOC\logs German XP: C:\Dokumente und Einstellungen\All Users\Dokumente\STALKER-SHOC\logs
The file itself is called xray_XXXXXX.log (where XXXXXX is your Windows login name).
If you open the file, you can either copy the whole log (extended log) or just the short log from the end of the file. It starts with FATAL ERROR - e.g.:
FATAL ERROR [error]Expression : 0 [error]Function : CPostprocessAnimator::Process [error]File : E:\stalker\sources\trunk\xr_3da\xrGame\PostprocessAnimator.cpp [error]Line : 221 [error]Description : noise.grain cant be zero! see postprocess [error]Arguments : nightvision_bad.ppe