Factual error: At some point Jack tries to get a message to CTU about the fact that he is being held hostage. The enemy sees Jack writing and tells Jack to shred the message. I work in government security. Believe me, no government agency would have a simple shredder that just cuts the paper into strips. Required is a cross cut shredder that breaks the paper into almost a pulverized state.
Character mistake: When Jack subdues Mason he proceeds to check his pulse to check Mason is still alive. When taking the pulse however Jack uses his thumb. This is not how a pulse is checked, as the thumb has it's own pulse and would therefore give Jack's pulse instead of Mason's. Being ex-Delta Jack would know this and not make the simple mistake. (00:22:10)
Audio problem: When we see the timer for the bomb on the plane, you hear the beep to indicate each second it clicks down. However, we see the timer say 24 seconds. We hear several beeps and 7 seconds later the timer says 20 seconds. The key point of the program being real time, so the timer should be on 17 at least. (00:37:30)
Visible crew/equipment: Jack Bauer and his boss are in a building at night with a shooter hidden somewhere. They open a door and look very carefully to the right and then to the left before going through the door. On the right side you can briefly see two crew members and as the camera pulls forward they back up some so they won't be seen. (00:23:50)