Mount type not recognised

I had a previous problem which I resolved by changing the mount type when i got this error to an already existing one in the vanilla game, however it is repeating with another model... Does anyone know what conflict stops the game recognising a mount type that you put in yourself? It's pretty much a copy and pasted model from a mod, the warhammer mod, im trying to add giants :/ they count as a mount type but the game does not pick up on them despite models/info/EDU etc being put in...

It says the error is in the EDU, "slavegiant" does not exist, but it is in the battle_model_desc and recruitable...