Continuity mistake: One of the 4400 now has an apartment and shows off her new darkroom to a friend. It has a sliding door at the entrance. In a later scene she is in the darkroom and her friend enters. But this time the door is a regular one that swings. In truth, neither of these are typical of a darkroom, as darkrooms have a light lock entry. Either double doors or a U-turn entry to prevent light from getting in.
Harlem's Renaissance Man - S1-E4
Continuity mistake: One of the 4400 is at the library looking at a newspaper headline on the computer. It says "Quicy Solarin..." A few shots later the same newspaper headline has been corrected to read "Quincy Solarin..."