Having a bit of trouble here on my second play-through, on the first level, I wonder if anyone has experienced similar.

I did Abigail's favour this time in the Rothwild Slaughterhouse and turned on all the valves to blow up the place, returned to her fine and my assassin popped up telling me she'd meet me outside. I exited the slaughterhouse via the sewer pipe in the huge captive whale room. As I start making my way back to the meeting point outside, up pops a "game over" screen citing "Irreconcilable Hostilities" as the reason I've failed.

Is this a bug, or have I done something wrong? This game over screen makes it impossible to finish the level, it comes up barely a minute after I've exited the slaughterhouse, and it never appeared on my first play-through when I chose a different option to blowing up the place.

Its not a bug. If Billie dies its game over. Try to reach the back alley(The one with the dead weeper)before the overseer executes her. Hope that helps I

Yeah like DrunkenWhaler said that if your sidekick Billie dies then that screens comes up. After exiting the slaughter house move quickly to save Billie from the overseers, You don't need to kill them just throw a choke gas and Billie will escape, It is faster and cleaner that way.

Thanks for the help. I decided to reload to a point before I'd finished turning on all the valves, then exited out of the main entrance instead. I'm assuming it was Billie that was causing it, but since the main entrance is closer to the alleyway she's in anyway I suppose I'll never know.