Summer Job - S7-E18
Continuity mistake: Mrs. Puff hands Spongebob the order for a Krabby Patty. In the next shot, he is not holding the order, nor is it on the floor.
Back to the Past/The Bad Guy Club for Villains - S7-E16
Continuity mistake: The Quickster was a member of the I.J.L.S.A in Mermaid Man and Barnacle Boy V. But in this episode, there isn't The Quickster in the I.J.L.S.A, but instead the Pi-Right Ponderer.
Summer Job - S7-E18
Continuity mistake: Mrs. Puff didn't know that SpongeBob works at the Krusty Krab, when she already found out in 3-18 "Krusty Love." Even stranger thing, Mr. Krabs and Mrs. Puff have no idea who each other are, but they also already met in that episode.
Answer: I believe this is the Season 6 episode "Spongicus".