Towards the end of the second part of the Taspir level after the sequence where you need to crawl through the conveyor belt I am having a huge problem. The doorway beyond that part is graphically glitched and whenever I try to pass through it shortly after I get the following error message:

CM_AdjustAreaPortalState: negative reference count

Anyone know a work around for this? Thanks in advance.

Sounds like you should install the latest drivers for your video card, and try to refrain from using any mods especially those which alter graphics/textures.