Factual error: When tracing the "Master Baiter" the detective says she can't trace the subject because "the HTML code is scrambled". There is no such thing as scrambled HTML, and on top of that HTML can never give away any information about a subject's location. Also, she can't get his IP address because it constantly changes. Yet, she does know from what exact wifi-spot he connected. If you get random IP-addresses, for instance by using random proxy servers, you can't pinpoint a location (which was of course why he used this technique).
Continuity mistake: When Donovan pushes Stabler off the roof, Stabler is standing with his back facing the parapet and goes straight over. However, when he's shown on the roof below after he's landed, he's turned almost a full 90 degrees and is lying parallel to the building.
Continuity mistake: Fin is talking to the suspect in the interrogation room. After he calls Fin a racist remark the camera goes to outside the room where Cabot and Cragen are watching in on them from the 2 way window. It then goes back to Fin with the suspect inside the room. When the camera points at the suspect you can see blinds are actually shut on the 2 way window behind him. So Cabot and Cragen could not possibly see in like they were supposed to.
Factual error: When Stabler's son Dickie is trying to join the Army, Dickie's recruiter tells Stabler that he can join at 16 with parental consent. This is incorrect, you have to be at least 17 to join the U.S. Army even with parental consent. Even if you could join at 16, the consent papers that Dickie bought to Stabler at the end of the episode can't be signed without a recruiter or notary public present and signing the papers at the same time. This is to prevent cases where a parent who had a change of heart can claim they didn't sign and to prevent 17-year olds from enlisting without consent by forging their parents' signatures.
Character mistake: In the scene where Detective Benson is presenting possible home care suspects for the rape of Cara, she says that Drew Cummings is on trial for distribution of Schedule 4 drugs. When asked which ones by Detective Stabler, she says "Vicodin, Percocet, Oxycontin, you name it..." Vicodin was a Schedule 3 drug, recently rescheduled to Schedule 2. Percocet and Oxycontin, the main ingredient for both being oxycodone, have always been Schedule 2. Schedule 4 drugs are drugs like Xanax and Phentermine, less addictive with lower legal penalties for distribution.