If that is the perk were you can upgrade Magical Armor, i have that one.
You should be able to get it to Legendary if you have 100 Smithing. Did you have enough Leather in your inventory? There are a couple of Vampire clothing items that cannot be improved, including the Vampire Lord Armor.
If you have trouble, try using a Fortify Smithing potion, and wearing some Fortify Smithing gear. If you don't have the required perk, you should still be able to get it to Legendary if you can Fortify your Smithing skill to 168.