Red Error

I downloaded some Lua addons and put them into my /addons/ folder, and they didn’t work, so I put them into the /garrysmod/ folder like it says if the /addons/ doesn’t work. Well I also have an /addons/ weapons addon that works, well every time I shoot, it shoots, but instead of discharging bullets, it discharges big red text that says ERROR. The file I first talked about is an NPC pack, and whenever I click the NPC I downloaded, it again spawns the big red ERROR text. Can anyone help me? Thanks in advance.

You are missing the model for the bullet/projectile.