Factual error: The murder victims, all Catholic, are specifically said to have "all worn crucifixes." But the jewelry Nat hands Nick as evidence, the cross that burns his hand and the necklace Magda later gives him are all plain crosses, not crucifixes. (The former is unadorned; the latter has a Christ figure on it.)
Visible crew/equipment: When the parish priest is preparing for the Easter Pageant and gathers up the bundle of sticks, the microphone dips into the shot at the top of the screen. (Aired version only. Mistake was digitally removed on the dvd.) (00:16:05)
Continuity mistake: While he's in the confessional, Schanke's raincoat collar is turned up. When he rushes out to confront Nick, it's folded neatly down again. (00:37:40)
Answer: Nick was sick and tired of being an immortal bloodsucker. He wanted to be human, fall in love, get married, have children, grow old and die. As for Janette, according to her, she fell in love and the passion she felt "cured" her of her blood lust.