Why can't I improve thief guild master armor set at the work bench?? I have my smithing skill at level 94. and my arcane smithing perk is unlocked so I should be able to improve magic apparel. And I have a sh1t tons of leather to use for improving thief guild master armor set. so why oh why can I not upgrade it??

edit: I used to be able to do it all the time in all my previous hundreds and hundreds of character. but yesterday i tried everything but it still doesnt let me. I even re start a new char and do all theif guild quest to get the guild master armor again. still can't upgrade it!! T_T

Strange...

I'll be back.