Other mistake: Toward the beginning, when the characters wonder aloud what the rumbling noise is, someone suggests that it's the ventilation system, to which Rennes responds "No vents." However, in the passages between rooms there are panels with ventilation slits in them (which you can plainly see even as Rennes says the line), and it's pretty impossible that the characteristically level-headed and observant Rennes wouldn't have noticed that.
Other mistake: After taking the CRS test, while talking with Feingold, Nicholas corrects his use of "unsatisfied" with "dissatisfied". Feingold responds, "That's right, you're a left-brain word fetishist." But earlier, on the phone with his ex-wife, Nicholas describes her growing family as "nucular" (as opposed to "nuclear" - the "cl" sound in the middle is key). Someone obsessive about word use would never make this mistake, it is classically seen as a sign of low intelligence and/or backward education. (00:11:55 - 00:19:50)Phoenix
Other mistake: When Kevin Spacey is lying on the carpet after having been killed by Jude Law's ghost, there is a very strange shadow visible to the left of the picture which looks as though it is someone standing there with their hands on their sides. There is nothing in the room to suggest that this is a shadow of a bust or a reflection of anything.