Factual error: The greeting message on the answering machine in German is spoken with an English accent. As Juliana grew up in East Germany she would speak German without an English accent.
Continuity mistake: The "Power Play" scene when Eric and Hanssen are in the car after a cancelled meeting (13). With Eric's line, "There's construction on E Street," the Kennedy Center appears behind his head, but in the next shot of him ("Sir, I'm SSG.,") the Kennedy Center shows up again, this time farther ahead of the car.
Factual error: When Kate is going to meet Eric, she is shown exiting the Federal Triangle metro station on the Blue/Orange Lines. However, for no apparent reason the signage has been changed to read incorrectly "Archives-Navy Memorial-Penn Quarter Station" which is actually on the Green/Yellow Lines. The blue and orange stripes on the station pylon have not been changed.
Continuity mistake: In the scene where Mr/Mrs Hanssen & Mr/Mrs O'Neil are all sitting own to have dinner together, directly after Eric being read in, Mrs Hanssen picks up all of the napkins to distribute them. In the next shot it shows one of the napkins back where she picked them up from, as if it was never picked up. In the following shot, it shows the same napkin laying vertically instead of horizontally.
Factual error: Early on in the movie there are boxes of new dell machines and moniters in the hallways. 3 things are wrong with this situation. First off, the design on the boxes is a newer design that was implemented in 2003, but the movie is set in 2001. Secondly, none of the monitors that you see in the office are dell monitors. 3rd, all the monitor boxes in the hallways are for flat panels (designated by the FP on the sides of the boxes), yet there are CRT monitors sitting on the desks. (I know about the box design because our company has a contract with Dell for our computers. I've personally done the ordering/config/setup since 2000).