I also had that problem in a second room. There's a linear path leading to the prison right?
I think that was a changing room for the guards or something on that path
And so far i didn't had any more problems concerning this issue
I'm now at a mission where i have to kill 2 guys & blow up a bridge or something
Also i heard alot of people complaining in reviews and such that the game is to difficult. The hardest part for me was mission 1 to understand how the ai works & the basics on how to obtain uniforms but i still think this game isn't that hard..
Maybe the assasinate 3 guys was a bit tricky but once you got the officercostume its a walk in the park.. Poison here, sabotage there with a trap on the door and boom 2 guys dead without even seeing there faces