Isn't that the part where you have to shoot the two security guards? Yeah, the mechanics in that are a bit weird, since you can't tell when the guards can stop and when they can't. While I think that the museum part is one of the best lead-ins to a game that I've seen, the way the game forces you to stay hidden kinda takes some of the charm away. Well, it's supposed to be a heist, so what else can you do?