Steam forums and Mod DB have indications that a recent Half-Life update may have broken mod support in Valve's first-person shooter. This originates from the creators of the Cry of Fear mod, and there are a couple of threads about support for that mod, and according to their post, the problem seems to impact other mods, and a fix may be out of their hands: "We're not sure if we can release a hotfix for these problems, since it's a lot of changes made to the engine that causes it." Thanks Ant.