I just started running a classic ASP site on IIS 8.5 and couldn’t get it working but wanted to know the error messages.   I was able to get error messages to be sent to the browser with the powershell as follows:

cscript %systemdrive%\inetpub\adminiscripts\adsutil.vbs set w3svc/AspScriptErrorSentToBrowser true

If you don’t have adminscripts installed, you can install them here:

• Start/(Settings)/Control Panel
• Set view to “Small icons” or “list” or “classic view”
• Choose “Programs and features”
• Click on “Turn Windows features on or off” in the left panel
• Expand (+) “Internet Information Services”
• Expand (+) “Web Management Tools”
• Enable all options, including “IIS Management Scripts and tools”
• Press OK and let Windows update.