In the X-Men: First Class movie, Sebastian Shaw holes himself up within the reactor chamber of his submarine. While in this room, Charles Xavier cannot sense or find him using his telepathy. He describes a "void" in the middle of the ship.
The walls of this room appear to be covered in mirrors. Once Erik begins smashing these mirrors (or more correctly, Shaw begins smashing them using Erik), Xavier can start seeing inside the room.
What is it about these "mirrors" that shut Xavier out? I am not aware of any instance in the comics where Xavier's telepathy was thwarted by standard mirrors.