Missing .mdl file while it's there?


I’m making a few cheap NPCs in Gmod, using the stalker exosuits models. A year ago, I made a few crappy new textures, duplicated the model files etc, hexed them with GCFscape and all, turning them into working npcs. Well, I decided to pick up that work and finish it. The NPCs have no animation errors so far, they work well but there’s a problem: once I spawn the ragdol. (When I go to browse -> addon name etc), you usualy find the models / props which you can spawn. Well, when I try to spawn the ragdol with the skin I edited, or the ragdol which I duplicated the .mdl (etc) files from -> I receive a LUA error, but the ragdol perfectly pops up as it’s supposed to be.

[gamemodes\sandbox\entities\effects\propspawn\init.lua:21] Models/srp/masterstalker.mdl

I’ve given these ragdols to friend/coder of mine, and took it to bigger heights. That’s why I need this error fixed.
I maybe know the cause, but I’m unable to verify: I didn’t use GCFscape to succesfully hex the .mdl files, I used notepad++
I used the same amount of characters, don’t worry. The reason I didn’t use GCFscape is because I’m unable to open the .mdl files with it, because of the “Unsupported Package” error.

If anyone would know the answer to this mystery, I’d be gratefull if you’d help me.