Continuity mistake: When Krabs', Squidward's and Puff's ancestors attempt to flee with the coach they pass way more buildings, seen in the background, than there actually are as shown in the overhead view of the town.
20,000 Patties Under the Sea/The Battle of Bikini Bottom - S5-E17
Audio problem: In "20,000 Patties Under the Sea" When Plankton says "Ah who needs that rustbucket anyhow!" his mouth is way out of sync.
20,000 Patties Under the Sea/The Battle of Bikini Bottom - S5-E17
Continuity mistake: In one scene where Spongebob is breathing in air, you can see the container to the right is yellow, but in the scene where he's dancing around the kitchen, it turns white.
Banned in Bikini Bottom/Stanley S. SquarePants - S5-E20
Continuity mistake: Banned in Bikini Bottom: After the chief of police tells his wife that he's starving he speeds off, and when it cuts to a closeup of the lock and chains, the wood plank directly behind the chains is crossed from upper right to lower left, but in the next shot it's crossed the opposite way. (00:05:40)
Banned in Bikini Bottom/Stanley S. SquarePants - S5-E20
Continuity mistake: Banned in Bikini Bottom: After the police raid the Secret Krusty Krab, Krabs and SpongeBob are both in handcuffs, but when Miss Gristlepuss trips and the Krabby Patty falls into her mouth, both pairs of handcuffs have vanished, then the handcuffs reappear again on Krabs. (00:09:45)
Banned in Bikini Bottom/Stanley S. SquarePants - S5-E20
Continuity mistake: Stanley S. SquarePants: When SpongeBob introduces Squidward to his cousin, Squidward's moai house has a doorknob at the right side of the door, but when Squidward loads the back of the moving truck the doorknob is at the left side of the door. (00:14:15)
Banned in Bikini Bottom/Stanley S. SquarePants - S5-E20
Continuity mistake: Stanley S. SquarePants: When Stanley's first customer tries to place an order Stanley pulls out a camera on a tripod, and in the next shot as Stanley hugs the customer for their first picture, the kitchen door behind them does not have the usual porthole, instead it has an anchor on it just like the door to Krabs' office. (00:19:15)
Banned in Bikini Bottom/Stanley S. SquarePants - S5-E20
Continuity mistake: In Stanley S. Squarepants, when Squidward moves out of the house with all his bags he doesn't shut the door, but when the shot zooms out, it's shut.
Banned in Bikini Bottom/Stanley S. SquarePants - S5-E20
Continuity mistake: In Stanley S. Squarepants, when SpongeBob and Stanley go see Squidward when he's getting the newspaper, both Squidward and the newspaper change position in between shots.
House Fancy/Krabby Road - S6-E1
Continuity mistake: Plankton's size changes drastically throughout Krabby Road. Plankton can be seen as reaching up to Spongebob's waist at one point. When he's clutching to the neck of a guitar, the amount of frets that go into his height change between one, two, three, and five, depending on the shot. (00:02:10)
House Fancy/Krabby Road - S6-E1
Continuity mistake: In House Fancy, Squidward gets a bad sofa injury. In the next shot, his feet seem fine.
Penny Foolish/Nautical Novice - S6-E2
Continuity mistake: In "Penny Foolish" around the beginning, SpongeBob does a lot of stunts before he picks up the penny. Then when Mr. Krabs flashbacks to what SpongeBob did, the buildings in the background change.
Penny Foolish/Nautical Novice - S6-E2
Continuity mistake: In "Penny Foolish" when Mr. Krabs is driving at night, there are a bunch of buildings surrounding him. Then when the shot cuts to the steering wheel and back to Mr. Krabs the buildings disappear.
Spongicus/Suction Cup Symphony - S6-E3
Continuity mistake: In "Spongicus" when Mr. Krabs and SpongeBob are outside looking at the "Chum Coliseum" and Mr. Krabs says "it's very suspicious" the tables inside the Krusty Krab are missing.
Revealing mistake: In "Not Normal" when SpongeBob says "Hmm. This video tape should help," his left arm is missing. (00:01:25)
Giant Squidward/No Nose Knows - S6-E7
Continuity mistake: In "Giant Squidward", Squidward goes to spray his wilting kelp with fertilizer and sets down a watering can right next to him. When the kelp goes back to normal in the next shot, the watering can disappears and is not seen again.
Giant Squidward/No Nose Knows - S6-E7
Continuity mistake: In "No Nose Knows", Patrick is trying out his new nose. He passes through a cloud of perfume sprayed by a fish in front of the perfume shop. In the next shot, the fish and the perfume shop are gone.
Boating Buddies/The Krabby Kronicle - S6-E9
Other mistake: In "Krabby Kronicle," when the two scientists exit Sandy's air dome, there are bubbles trailing behind them.
Boating Buddies/The Krabby Kronicle - S6-E9
Continuity mistake: In "Krabby Kronicle," when the female fish takes a copy of The Bottom Feeder, the pile of newspapers stays the same.
Boating Buddies/The Krabby Kronicle - S6-E9
Continuity mistake: In "The Krabby Kronicle", Spongebob takes a picture while holding the camera diagonally, but when the picture is printed, it is horizontal.
Answer: I believe this is the Season 6 episode "Spongicus".