Spawning Items throws eror and doesn't give item

I've been trying to spawn in a few custom items, and none of the ones I've custom made seem to want to work. I dont know what it is but every time I try to spawn in a custom item it throws an error in console and says an internal error has occurred. Sorry about the length, I'm not sure how to do a spoiler box.

Error:
Spawning Items throws eror and doesn't give item