MasterSen's Portal NPC Pack

I’ve downloaded the Portal NPC Pack, I OWN Portal, however it tells me that “You can’t spawn that NPC, sorry!”, is this because of an error in the files that the uploader failed to fix or is it perhaps a hardcoded mechanism that you can’t spawn NPCs that use Portal’s materials? Though that seems unlikely.

as far as i know that message only appears when you try to spawn npc’s that the server doesn’t have.

Right, it’s on singleplayer as well. I suppose I could download the extra NPC pack by the same author. It’s a shame there’s hardly any Portal NPC packs that have the turrets along with the sounds to go with it.