Revealing mistake: You can see devices under the water where the flames are when Jimmy first awakens.
Revealing mistake: When Lily hits the mirror with her hand, shattering it, the amount of blood on her hand in the next shot is too much to be realistic.
Revealing mistake: After Luc says "God is finally paying attention" at Rave-N-Fest, you can see an extra in the background, smiling in the next shot, which makes no sense after all the chaos that just ensued.
Revealing mistake: When Pestilence kicks the barrel, liquid starts shooting out, which makes no sense, as the contents are not under pressure.
Revealing mistake: When Jimmy flies out of the church, you can see his coat being pulled by a wire that was later taken out.
Revealing mistake: During the bar-fight, the bartender flies back and hits a table, and you can blatantly see the table is a breakaway prop, because there are no screws/nails or anything holding the top on. (You can see it easily just after the top gets knocked off.).
Revealing mistake: During the bar fight, after Jimmy knocks the gun out of Pestilence's hand, he hits him with the stick-weapon, but you can tell he missed Pestilence by quite a distance.
Revealing mistake: When Lily starts bleeding from the eyes at the end of the movie, you can tell the blood is not really coming from her eyes and was really just applied by a makeup artist.
Revealing mistake: When the bugs are flying into the bug zapper in the bar, the sparks on the bug zapper are far too big to be real, and are obviously small squibs set up on the zapper.
Revealing mistake: The scorpion Jimmy puts in the bag is obviously fake. It's arms and legs do not move at all, and it bobbles around like a rubber toy.
Revealing mistake: While at the wedding chapel, a shot is fired off camera in the other room, and we see the flash of the gun light up much of the chapel. But gun flashes aren't big enough to emit such light.
Revealing mistake: When War blows himself up, you can see a reflective material inside of the burning "crow symbol" likely to help contain the fire.
Revealing mistake: Right after Luc Crash becomes Lucifer, he combs his hair, but you can see he just lightly runs the wrong side of the comb through his hair, as so not to mess it up.
Revealing mistake: When Lilly's brother is firing at Luc and Lola, you can see the bullets hitting on the church behind them are too big and spark too much to be real, revealing squibs were used.
Revealing mistake: When there is the flash-montage of single-frame images at the bad-guy's hideout, you can tell many images are being repeated, and if you go through frame-by-frame, you can see some of them are actually behind the scenes photos of the cast interacting with the director/crew. (Smiling at the director off-camera, etc.).
Revealing mistake: When Jimmy breaks Pestilence's neck, it is very obvious he really isn't doing so, because he just bends the neck slightly to the side, in a very safe position.
Revealing mistake: When War shoots the fence, making the sparks ignite the liquid, you can tell in the shot from above the sparks were way above the liquid, and there is no way it would have ignited.
Revealing mistake: When Jimmy gets kicked by Luc the first time at the totem-pole yard, the kick misses him by quite a distance.
Revealing mistake: When War executes the wedding witnesses, we can see several people behind Lola, cowering behind a table, and they don't react at all when the shots are fired.
Revealing mistake: When War is firing the shotgun, the sparks from the bullets hitting the fence are ridiculously huge, revealing squibs were used.
Answer: As I understand it, it all had to do with a spat between the director of the original Crow movie (Alex Proyas, who had "approval" of all the subsequent Crow movies) the producer of the Crow movie franchise, Jeff Most, and Miramax. Miramax eventually caved in favor of the producer and it was made into a "non-Crow entity" when Miramax reportedly signed Eminem to play the bad guy.