Cannot get errors to show on IIS 10

I am writing some aspx vb.net scripts and cannot get the errors to show.  In my website root directory web.config I have:

<customErrors mode="Detailed" /> <compilation debug="true" />

But every time I get an error, it give me the error 500 page saying errors are not showing because customErrors mode="off".  Where do i find what is overriding this or what is the problem?