Visible crew/equipment: When the Zombies are chasing Greg in the woods, one of them leaps through the air. You can see the springboard he does it from. (00:45:25)
Revealing mistake: When Casper is pulled through the window with zombies hacking and chewing on her legs, her stumps end up as two clean cuts.
Continuity mistake: The rain comes and goes from moment to moment. This is especially noticeable during the extremely long shootout sequence where it is alternately raining/not raining between cuts.
Revealing mistake: In the laboratory, one of the supposedly gray, rotting, skeletal zombies lying on a table has a very visible pink, healthy nose sticking out of its skull. (01:06:30)
Visible crew/equipment: At the beginning of the 12-minute shoot-out, the camera pulls away from the group of protagonists in slow-mo. At the bottom of the screen, you can see the dolly-track that the camera is riding on.
Continuity mistake: In the end, the main monster is wearing Greg's face. When he pulls off his hood you can see a full head of hair and no creases, but seconds later when he pulls the mask off the mask only consists of the front half of the head, there is no hair attached at all.
Revealing mistake: During big gun fight to the house, if you watch in slow mo, a lot of the Zombies aren't attacking anything or anyone. They just appear to be running around randomly, or standing there like they're not sure what to do.
Audio problem: Kirk's accent changes throughout the film. Sometimes it's American, sometimes Irish, and sometimes Russian.
Continuity mistake: In the boat shootout, the same zombie (with the net on his back) is killed four or more times.
Continuity mistake: Note the final battle scene in front of the "house". That is, the house that was blown up earlier by a keg of gun powder.
Continuity mistake: Depending on what the zombies are trying to accomplish they either move veeeery slowly or at top speed, for example, when Kirk is on the boat, they swim with deft ability through the water but when they get on the boat and are ready to attack they move with stiff limbs.
Continuity mistake: When the swimmer-girl notices that her boyfriend disappeared and she walks back to the beach leaving the water, her back and chest are already dry.
Factual error: When the zombies are about to over-run the house, one of the ravers sacrifices himself by shooting a keg of gunpowder to blow up the building. The problem is that gunpowder is not an impact explosive, you could shoot that keg all day and all it would do is put holes in it. Just shooting it would not cause an explosion.