Character mistake: When Mr. Brooks and Marshall hack into the police database and are looking at detective Tracy Atwood's financial records there is a screenshot of the computer screen showing some very terrible spelling.
Continuity mistake: At the end of the movie as Michael Clayton is hailing a taxi, there is a silver SUV and a moving truck behind the taxi. As he gets into the taxi, the SUV and truck disappear and there are only yellow taxis behind his own. (01:53:30)
Factual error: At the very end of the movie, right before Javier Bardem is in the car accident, there is a shot out the driver's side window, past his face. In one of the driveways he is passing, a new Subaru Forester sits parked. The film is set in 1980.