I have nearly completed two playthroughs now and have twice encountered the same bug now. Brynjolf, the guy that normally gives the quest, just keeps saying to me that he is busy and therefor I can't start 'Under New Management'.
This really ticks me off because I still can't get the 'One with the Shadows'-trophy this way. I tried finding a solution to this on the internet but have so far only found things regarding changing console commands and what not for if you're playing on the pc.
I want to know if there is a solution for this problem on the ps3 or any way to start the quest anyway because this seems to be a pretty big bug to me.