Blood Money - S2-E17
Continuity mistake: When Sean sneaks back into the night club owner's office, we can see as he enters that there is no one in the left-hand side of the room. Yet, as Sean sits down at the desk, Walken somehow emerges from the left corner, which we have just seen was empty a moment before. (00:39:15)
Blood Money - S2-E17
Continuity mistake: When Nick and Schanke begin interrogating Sean, the tape recorder on the desk isn't running. It's going a few shots later, though, even though no one's touched it to turn it on. (00:30:30)
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.