Unable to use Solus Ipse Grand Visage as Monk Acolyte Chayula

Hello

I am unable to use Solus Ipse Grand Visage as a Acolyte of Chayula. I have all the stat and level requirements fulfilled. When I wear the helmet, it says, you cannot use this item, its stats wil be ignored.

Why is this?

Regards
Roccosplorer