IIS 7 and Above
IIS 8.5 Windows Authentication
Re: IIS 8.5 Windows Authentication
Feb 11, 2019 03:20 PM|Madness80|LINK
You need to tell IIS to display the details of the error. In the web.config file add the bolded lines to the appropriate sections.
<customErrors mode="Off" />
<httpErrors errorMode="Detailed" />
If that doesn't work, then you will need to enable failed request tracing for 500 errors. (You might want to do this anyway!) See https://docs.microsoft.com/en-us/iis/troubleshoot/using-failed-request-tracing/troubleshooting-failed-requests-using-tracing-in-iis-85
In that example they create an error situation for 404.2 to test with. You won't need to do that. Start at the "Enable Failed-Request Tracing" section and set it up for a 500 status code.