Achievement "I'm Gonna Live Forever" won't pop.

[OrphieBaby]

I tried two different save files. I got both helmets in Black Velvetopia, including the missable one. Every guide lists the same 6 helmets, and I didn't forget any of them. I am still unlocking new achievements, so that itself isn't bugged. I don't know what to do. It's frustrating enough that it's making me lose interest in continuing.

EDIT: I got the achievement. I uninstalled Psychonauts from my library in D: and installed it in C: . For good measure, I also did not enable the 9999-lives cheat. I do not know which of these two things fixed it. Also, correct me if I'm wrong, but... did you know they apparently patched it so that you don't lose lives if you fall off a cliff? That's good, because I've gamed over a few times due to that in the past, and everyone knows Meat Circus is a b****.