Texture problems with certain models

My Garry’s Mod has been having a lot of problems, such as the random black parts on models like the TF2 health-kits, also some of the L4D2 weapons look brighter than usual, does anyone know how to fix these problems? This happens for quite a lot of models, and I haven’t found anyone else that really has the same problem.

http://dl.dropbox.com/u/26908088/2011-04-19_00001.jpg