Corrected entry: Robin walks into the apartment and sees a goat turd, which can only be there if the goat was in the apartment. She goes on to talk to Marshall about keeping quiet about the fact that she slept with Barney, so we know that this happened when Ted was turning 30. But later in the end, Ted says that the goat was actually there on his 31st birthday. So the goat turd could not have been there at the time.
Corrected entry: In this episode we get to see when Ted met Marshall. But in Season 2, episode 1 Ted says to Marshall, "And there was my roommate, lying on the bed with his feet up on the wall. He had headphones on, big smile on his face. That guy was you." In this episode we get to see it was different. (00:04:40)IDFS33140
Corrected entry: In this episode Marshall and Lily buy an apartment that turns out to be crooked. When Marshall is hanging the picture it slants to the left of the camera each time he tries to straighten it, however the apartment is slanted to the right, on camera, and also demonstrated by Robin when she rolls the champagne bottle.
Corrected entry: The mystery woman warns Lily to stay away from Barney Stinson. When they go visit Anna, the second woman on the bracket, Barney reminds Lily that she thinks he's Ted Mosby. That would remove her as a candidate right away since Lily was warned to stay away from Barney, not Ted.