When Eddie is first taken into the security control room at the mall, the digital clock on the wall consistently changes between shots, going up and down. In one shot, the clock reads 8:48 and in the next shot a few seconds later, it has changed to 8:47.
At the beginning of the siege at the mall, the sniper shoots at somebody on the roof in rapid succession. This is not possible since he uses a single-shot rifle. In fact, when the scene switches to him you can see how he manually reloads the rifle.
Vance describes "Betty" as his "3057" for which he has a conceal/carry permit - even the subtitles say 3057. There is no such gun (since 1849) as a 3057. When it's produced later, Betty appears to be a 6" Colt Python .357 magnum - which is much to large for a practical carry-weapon.
When the protagonist calls his wife the dial tone heard on the phone is clearly not the dial tone that would be heard in the United States. It is a European dial tone indicating that the film was set, but not made, in the United States.