Error and Unauthorised pages...

Hey folks, for some reason when I navigate to a url that doesn’t exist on my site it’s redirecting me to the Unauthorised access page instead of the Error page. If I un-publish the Unauthorised page it will take me to the Error page as it should but for obvious reasons I want the 2 pages to work how they should. What can I check for any issues regarding this? My pages are set on different IDs in the configuration manager.