Asin's Creed Help?

if there are no objectives left try going in the in's bureau. If this still doesn't work, try going to your map screen and you'll see view options on the lower left hand part i think. if that's turned off you really won't see your objectives(eavesdropping,pickpocket,etc.… and in my opinion, your game is working properly because those barriers are supposed to be there to prevent you from going into the memory for the next stages(5th memory and memories after it).