Throughout the Series:

As the creepy "Nightcrawler," master vampire LaCroix taunts Nick via his CERK radio broadcasts, which Nick listens to on his Cadillac's car radio. Except... er... CERK's studio sign clearly says it's an FM station. And Nick's Caddy, supposedly a '62 (it's not, but that's another nitpick), still has its factory radio, which in 1962 was strictly AM. So how was he receiving LaCroix's station? Apparently, master vampires are powerful enough to make AM radios pick up FM signals!

The Cadillacs (all 3 of them) used throughout FOREVER KNIGHT as Nick's sea-green, cozy-trunk-haven, retro vampire transportation were not, as claimed in the show, 1962 models. Nick's car, in all its incarnations, was actually a '61. Creator producer Jim Parriott's tongue-in-cheek response to this gaffe, pointed out when the show was still on the air, was that the Caddies were just very good actors playing the part of a '62.

Though she wore medical smocks and occasionally a baseball cap to hold back her hair, Natalie was never correctly attired when she performed her autopsies. In fact, she usually worked with her hair loose and hanging down over the corpse, which may have made her look prettier, but is a serious breach of forensic etiquette that could contaminate the evidence. Even the best-coiffed coroners still have to wear sterile caps and gear.

 
Nick's old Cadillac had a handy dandy detachable dashboard police light, a siren and a mobile radio all added on so it could double as a police car. But no one ever thought to add a short-wave antenna, which should have been mounted somewhere on the car's exterior. The radio wouldn't work without it.
 

Dark Knight I & II

The blood stains on Nick's white turtleneck are lighter, then darker, then lighter again, and migrate to different positions, both during his fight with LaCroix in the abattoir, and throughout the hospital scenes afterward.

When Natalie shows Nick the murdered museum guard's bite wounds in the morgue, the "dead" man's carotid artery is pulsing quite healthily.

The murderer works for a blood bank and drives a bloodmobile, a plot holdover from the first pilot ("Nick Knight"), which was set in Los Angeles. This second pilot, however, is set in Toronto - and Canada doesn't have mobile blood units.

For I Have Sinned

While he's in the confessional, Schanke's raincoat collar is turned up. When he rushes out to confront Nick, it's folded neatly down again.
 
The murder victims, all Catholic, are specifically said to have "all worn crucifixes." But the jewelry Nat hands Nick as evidence, the cross that burns his hand and the necklace Magda later gives him are all plain crosses, not crucifixes. (The former is unadorned; the latter has a Christ figure on it.)

Dance By the Light of the Moon

The flashbacks to 1228 in this episode portray some of the same events - Janette seducing Nick, LaCroix making Nick a vampire - that are also shown in "Dark Knight." But here, Nick, Janette and LaCroix are all wearing completely different costumes.

Cherry Blossoms

In the flashback sequence, Janette calls the immobilized Nick "an immovable feast," a play-on-words reference to Ernest Hemingway's novel, "A Movable Feast." But this flashback is set in 1916. Hemingway's book was written in the 1950s.

Dying to Know You

Schanke calls Nick to tell him they've found Mrs. Hedges' body, and says, "They cut her throat, man." We even see a brief shot of the bloodied corpse. But later in the morgue, Nick says, "She was asphyxiated, right?" and Nat agrees. The corpse on the autopsy table now appears to have an intact throat. So, which way did Mrs. Hedges die?
 
Hunters

Nick's beard is fully grown in the beginning of this episode, but it changes, disappearing entirely more than once and then reappearing in various stages of growth, even in sequences supposedly occurring on the same night.
 
Father Figure

When the two henchmen who break into Nick's loft to kill Lisa are captured, the case is closed. But the two thugs were reporting back to a boss who wasn't caught, and who surely would have sent more hitmen after Lisa. So the case shouldn't have been closed.

Near the end, a cop comes to tell Schanke that an explosion has been reported at Nick's place. But neither of the two intruders uses any explosives. One shoots his way in through a door and the other breaks in through a skylight. Neither makes enough noise for the disturbance to be called an explosion.

Nat thinks Nick is becoming more human because he can see himself in the mirror, and he replies, "Only sometimes." This line contradicts series canon, as "Forever Knight" did not adhere to the vampires-don't-appear-in-mirrors cliché. Nick was seen to reflect very nicely, in fact, every time he passed a mirror, and not just "sometimes."
 
Dying for Fame

The insertion of a musical sequence used to fill extra time in this episode creates a plot problem. It's spliced in between Nick's urgent plea for Nat to stall the autopsy and his rescuing the bound and gagged Rebecca, and unfortunately makes it appear that in that interval, Nick simply went home, played music and sat in his loft window brooding, ignoring the case altogether.

Nick calls Schanke and asks him to take the Polaroids in to a lab for analysis. But Nick seems to have forgotten that he has the photos with him. They're not back at the precinct station for Schanke to take them in.

Forward Into the Past

Er, Maybe it was the 2nd Battle of Hastings? The biggest historical blooper in all of FOREVER KNIGHT occurs here, when Nick says to vampire archivist Aristotle, "You still owe me for that time at the Battle of Hastings." Nick was brought across in 1228, as the intro told us every week. The Battle of Hastings, as any British school kid could tell you, was fought in 1066, over 100 years before Nick's mortal birth. FK's producers apologized on line for not catching this goof, with the candid admission, "We blew it!"

Partners of the Month

When Schanke, in a huff, packs up his treasures and moves out of Nick's loft, he kicks the box of his belongings into the freight elevator, then gets in and closes the door. If you watch closely, you can see the cord of his duck lamp caught under the door, where it stays even after the elevator supposedly begins its descent. Oops!

Schanke's mother-in-law accidentally comes back from the dead here. She'd previously been established as dead, yet Schanke's talking to her on the phone in this episode. Actor John Kapelos says he told the director that Myra's mom was supposed to be dead, but was told to just shut up and read the line, because no one would notice. Wrong!

Spin Doctor

Speaking to Nat at the end, Nick refers to himself as "a certain indigenous vampire" with regard to his former life as an assistant professor in the U.S. Whoever wrote that line was apparently unaware of the meaning of "indigenous." According to my dictionary, it means "native to," and Nick wasn't native to either the US or Canada, where the show was set (he came from Brabant, now part of Belgium). If they meant "indigent," which essentially means "poor," he wasn't that, either. Maybe they were trying for "itinerant???" That means wandering, and he'd certainly done a lot of that in 800 years. Whatever they meant to say, they definitely chose the wrong word.
 
Fatal Mistake

The tow truck and the red van it's towing change positions at the alley's entrance between shots.

The wooden plank with which Alexandra impales Nick completely changes angles (from flat side tilted left to flat side tilted right) between the time it strikes him and the time he pulls it out. It also appears to "grow" an inch or so wider than it was before.
 
If Looks Could Kill

At the Precinct after the second spa incident, Captain Stonetree refers to "two unexplained reflex murders in one night." But the first victim survived the attack - so there was only one murder, not two. A little worse than a simple character mistake, since he's the police captain and knows the case. Schanke gets it right later, when he says, "One murder and one attempted murder."

Nick pronounces the plastic surgeon's name as "Yergen" in one scene and as "Jergen" in the next. At the end, she becomes Dr. "Yergen" again.

In the morgue, Nick tells Nat that vampires disappear when they die. Not so in this series. "Forever Knight's" vampires, defying old movie cliches, remained stubbornly intact when staked, making Nick's statement here a glaring contradiction of canon.
 
While in the Cadillac, Schanke says to Nick, "I can't believe you let me make a long distance call on your car phone." But what he uses to make the call is a large, early-90s cell phone, not a car phone. Car phones were wired and required a huge, boomerang-shaped antenna, a device with which Nick's Caddy was definitely not equipped.

I Will Repay

Janette tells Nick she's never brought anyone across (made them a vampire). Yet in the flashback to the 18h century in "If Looks Could Kill," she clearly made the baroness a vampire. Maybe Janette's "perfect" memory isn't quite as perfect as it ought to be.

Trivia: The piano piece Nick plays in this episode was composed and performed by Geraint Wyn Davies. He wrote it for his children, as an elegy to a pet bird that had died.

Elizabeth the leper is wearing a dirty gray dress under her black cloak - until Nick makes her a vampire, when suddenly there's a beautiful, spotlessly clean white gown under her cloak.
 
Love You to Death

The supposed ballerina in this episode's flashback to 19th century France is not employing any real ballet steps or arm movements. All she's doing on stage is standing still and waving her arms in the air, performing something that looks rather more like semaphore than ballet.

Queen of Harps

Nick and Schanke are interrogating a murder suspect and disagreeing about whether or not she did the deed. They leave the interview room together, and oddly enough, Nick's hair somehow manages to completely change styles as he walks out of the room. On the inside of the door, it's combed down over his forehead and rather "fluffy." The minute he exits on the other side of the door, it's brushed back and slicked down. Wow -- this guy is really fast with a comb!

[Thanks to Dot Simpson for remembering the right episode for the above goof!]
 
Curioser and Curioser

Trivia: All the sets in the dream sequence, particularly Nick's loft, are filled with props referencing Lewis Carroll's "Alice in Wonderland" books. They include white rabbits, flamingos, walruses, a squeaky-toy caterpillar - even a half-eaten piece of cake in Nick's fridge. The episode also has several background extras in Wonderland-style costumes, and numerous other references to the books, such as Nick literally falling through the looking glass at the end.

 
Killer Instinct

The cop who arrests Nick reads him his Miranda rights ("You have the right to remain silent," etc.) But "Forever Knight" is set in Toronto. At last report, Toronto rather resolutely insists upon remaining in the sovereign nation of Canada, where the Miranda Act, a U.S. Federal law, is not observed.

The re-use of a brief scene from the pilot episode, inserted during Nick and LaCroix's vampire battle in the warehouse, creates the unfortunate problem of Nick completely changing clothes in the middle of the fight.

When they're cutting up a roasted chicken during lunch break, Grace asks Nat to carve her a thigh and a wing. Even after repeating the request aloud, Nat hands her a drumstick instead.
 

Bad Blood

At the very end, Bridget Hellman is buried with a fully-engraved headstone in one just one day's time (which happens only in tv & movies: the process takes months in real life... er, death). She also spontaneously returns as a vampire without being "brought across," a violation of series canon, and she comes back mysteriously sporting 3 times more hair than she had as a mortal.

 
Black Buddha

In the flashbacks, the shipboard lifesaver rings are emblazoned with the incorrect designation "H.M.S. Titanic." The Titanic was a Royal Mail Ship. The stencil should have read R.M.S., not H.M.S.

Francesca

While the captain is speaking to Nick and Tracy, the Toronto Leafs hockey team coffee cup on his desk is sitting with the logo visible, until we cut to the detectives and then back to the captain. He isn't drinking any coffee and hasn't touched it, but now the cup is turned away from the camera so the logo is no longer visible. A few shots later, it's turned logo-out again.

I've noticed the following changes to the police station set, made by directors (I assume) for the sake of getting a particular shot. I'm making a distinction here between this sort of thing as compared to the miscellaneous changes that took place over time as the set evolved. What I'm talking about here is the deliberate mislocation of something which is thereafter put back where it belongs.

1. In Hearts of Darkness, when the press throng around the front desk, the swing gate at the end of the desk has been removed to facilitate the crowd scene.
2. In The Code, the coffee machine -- usually located at the end of the side corridor, down by the rear side exit -- has been put at the end of the inner wall, just beyond the water cooler.

One of my favs is in Father's Day:

The thugs storm Nick's loft in search of Constantine Jr. and riddle Nick with bullets. We actually see the bullets coming out of his back. But when Nick turns around to face the camera, there are no bullet holes in his vest.

For more of my Forever Knight bloopers, go to:
http://www.moviemistakes.com/tv5537