Revealing mistake: In the opening scene, when Van Damme kicks an opponent onto the boot of a London Taxi Cab, you can see the dent from previous takes.
Continuity mistake: When we first see Agent Holloway viewing the crime scene photos taped to the wall, he is facing camera looking at transparent pictures on a transparent wall (as if we are behind that wall, seeing through it). When the angle changes to see the Agent from behind, the photos are now paper photos on a normal, opaque wall and the pictures are arranged somewhat differently - most notably to Holloway's right near the top where two wider photos are vertically aligned atop and below each other in the second shot when they were misaligned in the first shot by nearly half their width. The transparency versus opaque materials issue is a stylistic choice of the director and not a mistake, but the mismatched alignments is a mistake. (00:11:25)
Continuity mistake: When King is fighting with Lazarus in the bar, Lazarus gets blood near his mouth like you get when getting hit in the face. But when they fight near the white door, the blood is gone. (01:13:00 - 01:18:00)