I also came to a dead end when I chose SULLY. I ended up going back to a previous savegame, chose JOHN, and was able to pick up the mug in Davie's office. I finished the game (Thanks to Mag), and had no more glitches. When Mag wrote the first version of the WT, it didn't mention the fact that the "choice" was that important. I then downloaded his second version, and that one made it very clear that you MUST choose JOHN at that point. Thank you, MAG. You must follow the WT VERY closely and choose the dialogues as Mag states in the WT, or else you probably won't be able to finish the game.
Sandy