Factual error: Bester lifts the blanket covering the bloody corpse of Harris' roommate. The man hasn't been dead long enough for the blood to dry, so there should be blood-transfer on the underside of the blanket - but there's not a spot on it.
Deliberate mistake: Though he moved freely about the station in his environmental suit, Kosh was never actually seen going through a door. He approached doors, but then, sometimes rather disconcertingly, would suddenly be shown on the other side. The reason: look closely and you'll realise his costume was too large to fit through any of the doorways on the set, so in reality the character would never have been able to move around the station.
Continuity mistake: At the security meeting, just as Captain Lochley is saying "I agree with Sheridan", she is shown in a long shot uncrossing her arms and starting to move forward. The camera goes to a close-up of her, and she once again is shown uncrossing her arms and starting to walk forward.
Continuity mistake: On Centauri Prime, Londo has an audience with the demented Regent. In the initial shot, the babbling Regent holds both hands up near his face as he speaks. In the very next, reverse-angle shot, his hands are down at his sides. When it cuts back, his hands are up again.
Visible crew/equipment: Approximately 29 minutes and 10 seconds into this episode, right after Sinclair clasps hands with "The One", Garibaldi and Sinclair are on the ground. In the upper right corner of the shot there is a grip with a red baseball cap and red and white shirt on. He has long hair and spiffy glasses.
Revealing mistake: Inside Sinclair's mind, just after the knight shoots the fake Garibaldi, he lowers his gun and the end briefly lights up red. Evidently the actor accidentally pulled the trigger on the prop and triggered the light that lets the CGI team time the effects correctly. Note that it is not the gun barrel glowing after shooting, as it is not lit up before he lowers it.