No Weenies Allowed / Squilliam Returns - S3-E6
Continuity mistake: In "No Weenies Allowed," when Spongebob gets punched by Patrick, he doesn't have a black eye. When the shot zooms to Spongebob's face, he has a black eye.
Big Pink Loser / Bubble Buddy - S2-E3
Continuity mistake: The broom that Patrick throws on the ground in Big Pink Loser disappears soon after.
Scaredy Pants / I Was a Teen-age Gary - S1-E13
Continuity mistake: When Spongebob is cutting his Jack-O-Lantern, he cuts out an eye on his right, but in the shot from inside the pumpkin the eye hole is gone, then the eye reappears.
Picture Day/Pat No Pay/Blackjack - S5-E13
Continuity mistake: When Patrick picks up the fridge and throws it on the barrel, there is some metal on the floor. When Mr. Krabs walks into the kitchen 2 seconds later, there is no metal on the floor.
Continuity mistake: When Patar heats the squished crab in the fire, it's in his left hand. But in the next shot when he eats it, it's in his right.
Wet Painters / Krusty Krab Training Video - S3-E9
Continuity mistake: When Mr. Krabs Gets Home, there is a light switch by the door, but in the next shot there is a sign instead.
Krab Borg / Rock-a-Bye Bivalve - S3-E8
Continuity mistake: Rock-a-Bye Bivalve: When Patrick gets home from the party after midnight SpongeBob is angry, and as Patrick walks out in the interior shot the front door is wide open on the inside of the home, but in the next exterior shot the front door is wide open on the outside of the pineapple.
Mermaid Man and Barnacle Boy IV / Doing Time - S3-E1
Continuity mistake: Mermaid Man and Barnacle Boy IV: When SpongeBob runs into the kitchen with Mermaid Man's secret utility belt, the door swings open facing away from the grill, but when Squidward demands to know what's going on in the kitchen, the door opens the opposite way.
Nasty Patty / The Idiot Box - S3-E4
Continuity mistake: Nasty Patty: After the police officer cancels his Krabby Patty order, when he tells his partner they got a call about "two ghouls burying a stiff," Krabs' office door is missing.
Nasty Patty / The Idiot Box - S3-E4
Continuity mistake: Nasty Patty: When Krabs pushes SpongeBob out of the kitchen telling him to pour on the charm for the health inspector, the door swings opens at the left side, but when SpongeBob goes back to the kitchen to order one of everything, that door opens the opposite way, then the switch happens again.
The Bully / Just One Bite - S2-E17
Continuity mistake: Just One Bite: After Squidward buries the Krabby Patty and tells SpongeBob that he hates it, when SpongeBob walks to the back door of the restaurant there's a window to the right of the door, but when Squidward makes plans to sneak a Krabby Patty that window has vanished.
The Bully / Just One Bite - S2-E17
Continuity mistake: The Bully: When Mrs. Puff enters the classroom and apologizes for being late, the door knob is at the left side of the door, but in following shots it's at the right side of the door.
Club SpongeBob / My Pretty Seahorse - S3-E12
Continuity mistake: My Pretty Seahorse: After Krabs tells SpongeBob the restaurant is not a place for a live horse, when SpongeBob walks out with the seahorse the swinging door to the Krusty Krab's kitchen opens in the opposite direction than previous shots.
Continuity mistake: Rock Bottom: After SpongeBob and Patrick enter the bus, when SpongeBob asks Patrick if he has any change and for the duration of this shot, both the gear shift on the floor beside the driver and the open door of the bus have vanished, then they reappear.
As Seen on TV / Can You Spare a Dime? - S3-E5
Continuity mistake: As Seen on TV: After SpongeBob shouts about the grand finale he tosses all the food at the hungry crowd, and as they all happily exclaim, "Krabby Patties," there is only one door to the right of Squidward's order station in this shot, though there should be two doors.
As Seen on TV / Can You Spare a Dime? - S3-E5
Continuity mistake: As Seen on TV: The front door to Mr. Krabs' office is a solid door with an anchor on the exterior side of the door, but in a few shots the office's front door has a porthole window like other doors in the restaurant.
Krab Borg / Rock-a-Bye Bivalve - S3-E8
Continuity mistake: Krab Borg: The door to Krabs' office has a porthole in many shots, but after Krabs burns his eyes he rushes out of his office into the eating area, and when he runs past Squidward and SpongeBob the office door is the normal solid door, with an anchor on the exterior side.
The Lost Mattress/Krabs vs. Plankton - S4-E2
Continuity mistake: Krabs vs. Plankton: When Krabs meets with the attorney, Bottomfeeder, both the exterior and interior door knobs on his office door appear and disappear in various shots, even consecutive shots.
Chocolate With Nuts / Mermaid Man And Barnacle Boy V - S3-E11
Continuity mistake: Chocolate With Nuts: While SpongeBob and Patrick are selling chocolate, the elderly female's door opens at the left, but after Patrick claims their chocolate will make you live forever, the door is open the opposite way.
Chocolate With Nuts / Mermaid Man And Barnacle Boy V - S3-E11
Continuity mistake: Mermaid Man And Barnacle Boy V: When Barnacle Boy shouts that he wants to be called Barnacle Man and demands respect, the door to Krabs' office is missing. Then it happens again when the news comes on.
Answer: I believe this is the Season 6 episode "Spongicus".