Patrick-Man!/Gary's New Toy - S9-E2
Continuity mistake: In "Patrick-Man", in the scene after Mrs. Puff gets arrested, the guy that SpongeBob serves the krabby patty to in the Krusty Krab is not wearing a T-shirt until the guy says "Lets hope Patrick Man doesn't confiscate this one," then he is seen wearing a white T-shirt. (00:08:00)
It Came from Goo Lagoon - S9-E7
Continuity mistake: The apparel of the fish at the top of the water-skiing pyramid at the start changes between shots.
Little Yellow Book/Bumper to Bumper - S9-E4
Continuity mistake: In "Bumper to Bumper", Mrs. Puff gets out of the boat and asks Spongebob to switch seats with her, and Spongebob is wearing his seat belt. In the next shot, once she has made her way around the boat to the side where Spongebob is sitting, he is no longer wearing his seat belt.
The Fish Bowl/Married to Money - S9-E18
Continuity mistake: In "The Fish Bowl", Sandy has a wristwatch on her right wrist when she first appears on the bus. When she sits near the front to observe the fish, the wristwatch has disappeared and doesn't reappear.
The Fish Bowl/Married to Money - S9-E18
Audio problem: In "The Fish Bowl", after Patrick takes the bowls of ice cream and eats them both, he throws them behind him. The bowls just disappear in mid air without leaving the frame (also an "other mistake") but the sound of the ceramic bowls breaking is still heard.
The Fish Bowl/Married to Money - S9-E18
Continuity mistake: In "Married to Money", Pearl cries and her tears flood Mr. Krabs' house. When this happens, he pulls a in the floor to let the water drain. In a few shots, this plug and drain are missing.
Sold!/Lame and Fortune - S9-E21
Continuity mistake: In 'Lame and Fortune', a big box of fortune cookies drops in SpongeBob's backyard. When Gary goes to read his fortune, he leaves a slime trail. However, the slime trail disappears and reappears between shots.
Answer: I believe this is the Season 6 episode "Spongicus".