Deliberate mistake: When Eddie and "Jennifer" are walking around the house alone, she is trying to tell Eddie that she's really Sara. But by the time she is explaining that, Eddie has disappeared. She doesn't find him until later. But from the moment she finds him (and he is talking to her) he calls her Sara, despite never actually hearing her say that. Also, after they all get back together, a few of the other people start calling her Sara as well, but no one actually heard that either.
House on Haunted Hill (1999)
Ending / spoiler
Directed by: William Malone
Starring: Famke Janssen, Geoffrey Rush, Taye Diggs, Peter Gallagher
Everyone dies from a huge ghost of everyone that died in the building, except Taye Diggs and Ali Larter. Chris Kattan's ghost helps them escape right in the nick of time. They both end up on the roof and find all the checks. Taye Diggs and Ali Larter were the only ones not related to people that died in the building years ago.
ugly bob
More mistakes in House on Haunted Hill
Evelyn: You know if you really love me, you'll find a way to drop dead in the next three seconds.
Stephen Price: Finding ways for me to die is really your deal, isn't it Eveline? Let's not forget the OJ knife with the not-quite-retractable blade. Your Jim Jones Kool-Aid was exactly that.
Evelyn: Accidents, all accidents until proven otherwise.
Trivia: The Terror Incognita roller coaster is actually The Hulk roller coaster in Universal Studios, Orlando.
More questions & answers from House on Haunted Hill
Answer: The Darkness thought he was lying to save himself, everyone killed had the seven deadly sins. Greed, Lust, Envy, Sloth, Gluttony, Wrath and Pride.