After I unequipped the Enlightenment Stuff from my apprendice, the game won't let me equip it anymore saying that it's "Not valid for the current hero" even if I'm using a level 50 apprendice.

I've tried swapping hero, unequipping all my items and equipping them back again, reloading the game. Nothing works. Please adress this issue, I really need be able to use that item again.