Hall Monitor / Jellyfish Jam - S1-E7
Continuity mistake: In "Hall Monitor" when SpongeBob is pretending to be the "open window bandit," you can see a red piece of coral outside of the house that he is about to break in to. When he jumps through the open window, frightens the people inside, and they run out of the house, the red piece of coral is gone.
Sandy's Rocket / Squeaky Boots - S1-E8
Continuity mistake: When SpongeBob is explaining why he thinks there are aliens in Sandy's Rocket, you can see a plant and rocks. We see a wide shot and it has now disappeared. (00:02:00)
Sandy's Rocket / Squeaky Boots - S1-E8
Other mistake: In the episode "Sandy's Rocket", Spongebob and Patrick go "alien-hunting." SpongeBob and Patrick are in Squidward's house. But when SpongeBob holds the hot water bottle, and he says "No, it's an egg-sack!", one of the drops leaking from the bottle goes up instead of down.
Sandy's Rocket / Squeaky Boots - S1-E8
Continuity mistake: In "Squeaky Boots", Mr. Krabs starts hearing squeaky sounds everywhere. Then he goes mad and says he took the boots from SpongeBob. At this point, notice the restaurant floor's colour. Mr. Krabs lifts the whole restaurant, but we can still see some floor (where Krabs is). Notice that now the colour of the floor has changed.
Sandy's Rocket / Squeaky Boots - S1-E8
Factual error: Sandy's dome is both airtight and watertight to keep any water out of the dome and any air inside the dome. When the rocket, positioned outside of the dome, begins to launch, smoke is coming inside the dome. This shouldn't be able to happen if the dome is airtight and watertight.
Sandy's Rocket / Squeaky Boots - S1-E8
Continuity mistake: When Pearl is opening her present the cake disappears.
Sandy's Rocket / Squeaky Boots - S1-E8
Continuity mistake: Sandy's Rocket: When you first see SpongeBob in bed you can see a mysterious glass window on the floor. When Patrick arrives it has vanished, evident in the wide shot.
Sandy's Rocket / Squeaky Boots - S1-E8
Audio problem: In "Sandy's Rocket", when Sandy says "Aliens? Is that what this is about?" her mouth stops moving halfway into her sentence.
Sandy's Rocket / Squeaky Boots - S1-E8
Audio problem: When SpongeBob captures Mrs. Puff, her voice and the inflation sound are out of sync.
Sandy's Rocket / Squeaky Boots - S1-E8
Continuity mistake: In "Squeaky Boots", a piece of Mr. Krabs's foot comes off in a hole in the floor boards. Several shots later, it disappears by itself.
Sandy's Rocket / Squeaky Boots - S1-E8
Continuity mistake: In "Squeaky Boots", Mr. Krabs is about to reach a curve in his boat, but in the next shot, he continues driving straight.
Nature Pants / Opposite Day - S1-E9
Continuity mistake: When Spongebob goes to answer his door, Patrick was obviously in front of the door. After Patrick says, "Spongebob doesn't like me anymore", it cuts to a different shot to show the outside of the front door, and Patrick has moved to the side of the door.
Nature Pants / Opposite Day - S1-E9
Continuity mistake: Opposite Day: The front door knob on Squidward's house repeatedly switches between the left and right side of the door, so it opens the opposite way (it has nothing to do with it being opposite day).
Nature Pants / Opposite Day - S1-E9
Continuity mistake: In "Opposite Day", Spongebob pushes Squidward through the sand, leaving a pile of sand. Two shots later, they are now on Spongebob's sidewalk and the sand pile has disappeared.
Nature Pants / Opposite Day - S1-E9
Continuity mistake: In most of the show, Squidward's house only has windows on the front of his house. But, in "Opposite Day", he has windows on the "ears" of his house, which don't appear throughout the show.
Nature Pants / Opposite Day - S1-E9
Continuity mistake: In "Nature Pants", Spongebob comes back home, where his friends have thrown a "Welcome Back" party for him. When he enters, two balloons float behind him. In the next shot, they disappear.
Culture Shock / F.U.N. - S1-E10
Revealing mistake: In "Culture Shock" when Spongebob takes the green fish's order, he has a pencil tucked in his ear, but he doesn't have an ear, so it's just floating in thin air. (00:01:55)
Culture Shock / F.U.N. - S1-E10
Continuity mistake: When SpongeBob and Plankton jellyfish,SpongeBob catches a jellyfish with no spots. Then it shows the jellyfish with spots or vice-versa.
Culture Shock / F.U.N. - S1-E10
Continuity mistake: In "F.U.N.", Mr. Krabs sets down the Krabby Patty in front of Plankton. Almost the whole plate is on the yellow part of the table, but when the camera cuts to Plankton, the plate is mostly in the red part of the table. In the next shot, the plate returns to its original position.
Culture Shock / F.U.N. - S1-E10
Continuity mistake: In "F.U.N.", Plankton uses a laser to get through the secured Krusty Krab. When he does this, we can see the outside. In the next shot, the hole is now gone.
Answer: I believe this is the Season 6 episode "Spongicus".