I won't provide specifics as to not spoil anything for anyone, but here is the Jist of it. To Clarify, this is on the PS3 and Xbox versions, ONLY. The PC Version can be fixed via Console Commands.
Later on down the line in the Thieves Guild quest line, you are required to present a piece of your armor they gave you when you first joined. Myself, like 75% of the people who play, ditched that armor long ago in favor of Dragon, Daedric or Nightengale. Unfortunately, without this quest being completed, you are unable to become the Master of the Thieves Guild, and thus are unable to finish the quest series. There is currently no way to re-obtain the armor or purchase a new set. I really hope there is a fix in the works for this.


