it's a Daedric weapon, so you need the Daedric Perk.
I have that perk too.
Most of the unique items given out by the daedric are not governed by the smithing perks. So you have to have 100 skill + smithing gear and a smithing potion to bump your effective skill up high enough to make them legendary.
Ok, that must be it, thanks. As the perks I dont have are on the light armor side, and I dont see why this hammer would be elven / glass