If u sell your thieves guild armor, and u cant get it back, then u cant use tonilia as a fence and complete the thieves guild questline. This should be a priority fix, its very annoying, but i havent encountered any major lags with over 50 hours of gameplay so far, but these glitches with no way out should not happen

http://www.gamesas.com/topic/1322361-thieves-guild-major-glitch/page__p__19880358#entry19880358