User-460007017 posted
Hi Knoelen,
Your error page only show the simplified error page or just page can't display? If it display the page can't display, then you need to check your website configuration.
If It show the simplified error message, did you configured the error message like steps in following link?
https://blogs.msdn.microsoft.com/rakkimk/2007/05/25/iis7-how-to-enable-the-detailed-error-messages-for-the-website-while-browsed-from-for-the-client-browsers/
The error page also need to be configured in the site level instead of the global server level.
Besides, please test the error message in IE explorer and disable the
Show friendly error messages in Internet option->advanced.
Best Regards,
Yuk Ding