The amount of blood spill on Kyle's face and shirt changes between shots.
(at around 1 min) In the beginning of the film which shows a recreation of the opening scene from House on Haunted Hill (1999), Dr. Vannacutt is performing a vivisection on a patient while a nurse films him. In the previous film, there was a second nurse who was assisting him.
Norris first grabs Ariel by her hair when he is taking her hostage in her house. In the next shot however, he is grabbing her by the back of her shirt.
Ariel's staircase is shown with no handrails or banisters, but this doesn't comply with the building code in place in California in 2007.
(at around 53 mins) After escaping from Ariel and the others, Desmond and Michelle walk into a room with windows and the rainstorm outside is clearly visible. Since the building was in lockdown, the metal plates/shutters should have been in place, thus preventing a view of the outside.
(at around 41 mins) Ariel refers to the 5 employees who survived the fire that occurred in the asylum in 1931 as orderlies, which they weren't. They were: Ruth Anne Stockard (head nurse), Thomas Steven Price and Adolphus Jenzen (electroshock), Jasper Marr (hydrotherapy) and Franklin Baker (pathologist).
(at around 1h 13 mins) In the end, Ariel refers to the evil events leading up to the fire in the asylum as taking place over 50 years ago. The sequel takes place in 2007 and the fire occurred in 1931, which is actually a span of about 76 years.