Jack is seen being forced to load a rifle round into the assassin's weapon. Later, the assassin loads the weapon again, this time with a .45 pistol magazine. The two types of rounds can't be compatible with the same weapon, nor does it make sense to load it twice.
Kim wears pink strappy wedge-heel sandals from the beginning of the series until her rescue, yet in one shot in the barn she is suddenly wearing pink slippers with dark socks, then in the next shot she is wearing the sandals again.
After assembling the rifle, Jack takes out his gun and points it at the photographer, but he couldn't have a gun on him since he has passed through a metal detector before entering in the restricted zone of the building.
After Almeida lets Myers back into the building and takes her to a room without any active cameras, he tries to call the Secret Service from an unplugged phone (Cisco IP phones illuminate the display when the receiver is lifted. If the display stays dark it's because the phone doesn't have power).
When Nina is calling CTU (at around 12 mins) her watch is visible showing the time to be 09:25. This episode takes place between 07:00 and 08:00.
Jamey's supposed to be receiving messages using her PDA. However, you can clearly see "Memo X of 3" above each of the messages, showing that they were pre-written onto the PDA.
After Nina tries to call Jamey at CTU from the abandoned warehouse a cameraman is visible on the right side, moving in on Nina.
(at around 4 mins) When "Belkin" is walking up to security a camera and cameraman are blatantly in the shot filming him.
When Jack is checking into the breakfast, he approaches Aaron Pierce, At the same time a lot of the crew and several pieces of equipment are visible on the right side and can still be seen a few seconds after.
(at around 22 mins) One of the cameramen following Jack gets too close and moves into the shot, along with part of the camera. 15 seconds later, he shows up again.
(at around 31 mins) Part of a camera enters the shot when Nina walks around the table.
(at around 24 mins) When the camera pans over Tony and Nina's hands, the boom mic is visible at the bottom of the frame.