<configuration>
<system.webServer>
<httpErrors errorMode="Detailed" />
</system.webServer>
<system.web>
<customErrors mode="Off" />
<compilation debug="true" />
</system.web>
</configuration>
Exception message: c:\webroot\hitekfab\dmxConnectLib\li b\zip\zip. aspx(9): error CS0246: The type or namespace name 'Ionic' could not be found (are you missing a using directive or an assembly reference?)
try go to Event Viewer and see if there's some application errors recorded there?
also, try to change if there's any web.config, so to show the exact error on the page.
for example:
Working past 500–Internal server error
https://blogs.iis.net/rickbarber/working-past-500-internal-server-error