Plot hole: In "Once Bitten", Mr. Krabs never unlocks the doors to the Krusty Krab, but at the end of the episode, Squidward enters with no problem.
Continuity mistake: In "Once Bitten", Mr. Krabs is holding a key, about to unlock the doors to the Krusty Krab, when a customer stops him. Two shots later, the key is missing from his hands.
Continuity mistake: In "Once Bitten", there is a keyhole on one of the doors to the Krusty Krab. Several shots later, the keyhole disappears.
Continuity mistake: In "New Leaf", When Mr. Krabs throws Plankton's snow globe in to the room, there is no lock. In the next shot, there is.
Suggested correction: Maybe Squidward has a key to the Krusty Krab that Mr. Krabs doesn't know about.
ccoccia
Absolutely not. There is a very clear shot of Squidward pushing the doors open without a key.
zenee
He could still have a key, but we don't see it.
Whether or not Squidward owns a key to the Krusty Krab is beyond the point of the mistake here. The point is that Squidward is able to walk into the Krusty Krab despite the doors being locked, and he doesn't use a key or anything else to unlock them. He just pushes them open.
zenee
Maybe the doors were not locked properly.