Peter doesn't seem to know what an Imp is even though he encountered one in "Janine's Day Off."
After Ray hangs a "Closed" sign on the door of the Joke Shop, it disappears for a couple of frames, then reappears again.
When Ray is getting Ecto-3 ready, as he pulls the cord, the flag and part of his proton pack are missing for a few frames, then suddenly appear.
When three of the Ghostbusters run to Ecto-2 at the dock, there are two Egon's and no Winston. Winston has Egon's colors by mistake.