Factual error: In the scene where the cast find the guns in the tiny coffins, they mention that it is not possible to tell if they are loaded because the clips are welded. Being semi-automatic pistols, simply pulling back the slide & ejecting the first round would have easily determined whether live or blank rounds had been loaded.
Factual error: Pretty precisely at 46:20, in the scene where Eddie and Sarah lost sight of each other down in the cellar, Sarah follows the apparition she thinks is Eddie. While doing so we see writing at a wall: "stehen nicht bei türen oder fenster wann dem Alarm gehört war" . The sentence contains so many mistakes that it's difficult to understand, but it roughly translates into "don't stand in doorways or windows after hearing the alarm". But it's a cellar, so there shouldn't be windows, and if the reason for the warning is the locking device: that closes only exits, and there are none of those in the cellar.
Factual error: At the opening scene of the film when one of the insane people of the institute shoves pencils into the guys neck, the pencils we see are not long enough to go right through his neck. The insane patient would have to be holding the pencils inside the guys neck for them to go right through him. (00:04:40)