Hello, Bikini Bottom/Extreme Spots - S8-E29
Continuity mistake: In "Hello, Bikini Bottom", when we see Mr. Krabs' list of what he needs for the tour, the word "roadie" is on the bottom of the list, but when we see the list again later on, "roadie" is in the middle of the list.
House Sittin' for Sandy/Smoothe Jazz at Bikini Bottom - S8-E23
Continuity mistake: When Sandy finds SpongeBob and Patrick after wrecking the tree dome, the distance between SpongeBob/Patrick and Sandy changes constantly between shots.
Karen 2.0/InSPONGEiac - S8-E28
Continuity mistake: Karen dumps a load of chum on a tray and some of the chum lands on the table. The chum that fell on the table magically disappears from shot a split second later.
The Krabby Patty That Ate Bikini Bottom/Bubble Buddy Returns - S8-E15
Continuity mistake: The giant Krabby Patty eats SpongeBob's shoe and sock in the kitchen. But by the time SpongeBob and Squidward run to the door and are stopped by Mr. Krabs, the shoe and sock have magically reappeared.
Mermaidman Begins/Plankton's Good Eye - S8-E22
Continuity mistake: When Plankton tries to open the safe, his arms come off. The arms stay on the safe. But when Mr. Krabs approaches the safe in the next shot, Plankton's arms have disappeared from the safe.
You Don't Know Sponge/Hide and Then What Happens - S8-E3
Other mistake: It is revealed in this episode that Patrick is right-handed. However, in the season 4 episode Krusty Towers, when asked to sign the Krusty Towers guest register, he is shown doing so with his left hand.
Ghoul Fools - S8-E24
Continuity mistake: When Squidward is sucked into "The Void", the bag of money that he was holding vanishes in the next shot.
Audio problem: When Spongebob, is in the pile of rubble left after Squidward unraveled, he picks up his phone receiver. Then, Gary slithers away and you hear Spongebob pressing the keys on the phone, but when it cuts back to him, he is only holding the receiver.
Answer: I believe this is the Season 6 episode "Spongicus".