That sure is a misterious message, could mean a lot of things, I am sure one of them is that it didn't find any animation called "idle" in the folder, but that's just my take on it, maybe it's mispelt.
Revert to the old syntax in post 1. This is correct 'code'. You could even remove the activity keyword when it starts with ACT_XYZ. Is it possible the activity is ignored? It's sorta defining the start of the definition twice. Could be a glitch in the compiler. Do the idle and draw activites trigger? Possible they are from a shared animation file? You may have to check. i got no clue how gmod works.
The other question is what's in the animation files. Are there working animations in it? Also. I thought to know old hl2 models have a system inplace which recycles and blends shooting animations with a crouch pose, blend layers, aim layers and parameters. There's a potential chain of dependencies to make the entire shooting animation work. Again, i got no real clue. 'm not a game modder.
I put idle01 and nothing. Same problem...
bump
Bumping a still live thread are we eh?
Well, the error message says that Idle is absent, NOT idle01, you have to add an animation called "idle.smd" in the folder it's directed at, in this case c_rinkaku_hand_anims