After Johnny Layton (Dave O'Brien) shoots and kills one of the devil bats, the article in the Chicago Register states his name as Henry Layton, while another one in the Springfield daily correctly names him as Johnny.
The goof items below may give away important plot points.
When reporter Johnny Layton shoots the first "devil bat", a shot follows of the front page of a newspaper which says "Reporter Kills Devil Bat". In the first paragraph the reporter is identified as "Henry Layton".
It is established that the Devil Bat attacks are targeted to certain scents, yet when Lugosi "marks" his first victim by pouring the lotion into the man's hands and having him splash the lotion on his neck, he then shakes hands with him and immediately goes to release the bat - which does not seem to mind the scent of the lotion on Lugosi's hand.