Factual error: Toward the end of the film, Matthew McConnaughey is in his office late at night and hears someone outside (it turns out to be his wife). However, McConnaughey draws a revolver from his desk drawer and we can hear (but not see) him pulling the hammer back to cock the gun. Problem is: When pulling back the hammer on a revolver, the cylinder turns to rotate the next bullet into position. The cylinder did not turn. The sound we heard was obviously added by the sound editors after the scene was shot.
Audio problem: When "Mickey Mouse" rescues Roark, he says something like "It's gonna be all right," yet his mouth is closed and not moving at all.
Continuity mistake: At the end of the movie when Sandra Bullock character is in the hospital and the nurse revealed to her that Carl Lee was innocent, look carefully at the TV. You can see Jake, Harry Rex and Lucent standing outside the courthouse, but in the very next scene they haven't even left the courtroom.
Character mistake: The sheriff has his service weapon on him in the cellblock. Whenever law enforcement enters a jail or prison, they disarm.
Continuity mistake: The DA addresses Deputy Looney in court as "Detective". He is a uniformed deputy, not a detective. It would be surprising for a lawyer in court to make such a mistake.
Suggested correction: Looney is not in uniform at the time of the trial, though. It's not that he doesn't know his rank; he does refer to him as deputy when he is first called to the stand. As the district attorney, I'm sure he has likely needed to cross-examine many deputies and detectives. This is a simple character mistake: just a slip of the tongue, and a rather understandable one.
Character mistake: At the end, the sheriff arrests his corrupt deputy. Why wouldn't he remove his equipment and search him?