I still have this very problem. If I run gmod from "original" wine (any current version), works just fine. Just to check: I symlink steamapps folder to both cx games steam and wine steam.
Here is what it looks like:
Seems that this error is from the engine itself, and is generated by mis-configured mods, but since it's oficial gmod, i'm running in wine and i'm the only one having it on cx games... I must be the One.
My system is ArchLinux, KDE 4.3.4, X.org 7.5, X.org server 1.7.3, nVidia drivers 190.42, kernel 2.6.31
This has been affecting me since CX 8.0, which included older kernel, x.org and drivers (might not be a bug in those)
Well.. If anybody else has this problem, just shout. It's tedious to be alone...