Cant equip?

[TidusVsSora]

I just got the item Dark Wings, and i want to equip it. problem is, it says i cant for some reason. I'm a fighmaster level 60 and my armor has the required slot (extra slot).
am i missing something?^^;

[Volcompat321]

Do you have S rank armor?
If you have A it wont be able to equip.