General Kellner is wearing his ribbons on the right, when it should be on the left.
U.S. Marines are shown guarding the embassy perimeter. Usually that is guarded by local police.
Spelling and grammar mistakes in in-game text.
The Player is given the ability to destroy security cameras. Doing this should raise the suspicion of whoever is operating the camera.
Mr. Fisher's gear has a radio and night vision goggles, both of which glow and would give away his position.
The Player is tasked with bugging Sadora's telephone. However, in order to complete the mission the Player must bug Sadlra's computer.
Lambert can be seen getting a vaccination for small pox between mission 4 and 5. Lambert was born in 1961, meaning he attended primary school in the mid 1960's and early 1970's. At that time school children were routinely given several vaccination, including small pox, making the vaccination unnecessary and wasteful. Nearly all Americans over about 30 in 2006 would be immune to that virus.
U.S. soldiers are shown wearing M1 helmets in 2006. These were long replaced with the PASGT by the 2000s.
In mission 1, Grimsdottir says "worse" but the caption says "worst".
The truck at the LAX level in California has European Union license plates.
During a news scene, Vietnam is labelled as Laos.
In the first level, Lambert tells Fisher of all the things his suit does. He already knows all this, having been through it before so it would be redundant to tell him again.
In the mission 1 intro cutscene, Lambert says that the NSA called him. He's in the NSA so it would not make sense for him to refer to the NSA as if it were a separate entity.
The news anchor says "Delta Forces", but the proper term is "Delta Force".