After seeing the Yes Man and showing him the chip, I'm greeting by a man when I leave The tops Casino. He tells me to go see Caesar at Fortification Hill and gives me the Mark so I won't be attacked. As soon as I get there, I'm attacked. I put on one of the Legion's amour as a desguise and I can get past a few people. But when I walk into Caesar's tent, everyone attacks me.

What's the dealio?