Corrected entry: When Shaggy is driving with the zombie on top of the van and he stops suddenly, the zombie flies off the roof and lands in the dirt. But in the next shot, he's leaning up against a tree.
Corrected entry: When Shaggy and Scooby are in the storage room, the phone rings and it turns out that it's Fred who is calling them. This makes no sense, because Shaggy and Scooby were merely in that room by coincidence, so there's no way Fred could have known they were there.
Correction: The zombie is leaning against the tree in every single shot.