Cannot add duplicate collection entry of type 'add' with unique key attribute 'name' set to 'aspNetCore

Question

I have recently published my ASP.NET Core application to my host. I am hitting a HTTP Error 500.19.

IIS 8.5 says the issue is:-

"Cannot add duplicate collection entry of type 'add' with unique key attribute 'name' set to 'aspNetCore'"

It also highlights this key add line in my system.webServer config:-

<handlers>
  <add name="aspNetCore" path="*" verb="*" modules="AspNetCoreModule"      
</handlers>

I'm not really sure what to do on this. It looks as though there is a duplicate instance of this, so I have tried renaming this but it still asks to add this again?

Here is my web.config:-

<?xml version="1.0" encoding="utf-8"?>
<configuration>

  <!--
  Configure your application settings in appsettings.json. Learn more at http://go.microsoft.com/fwlink/?LinkId=786380
  -->

  <system.webServer>
  <handlers>
    <add name="aspNetCore" path="*" verb="*" modules="AspNetCoreModule" resourceType="Unspecified" />
  </handlers>
  <aspNetCore processPath="%LAUNCHER_PATH%" arguments="%LAUNCHER_ARGS%" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" forwardWindowsAuthToken="false"/>
  </system.webServer>

<system.net>
<defaultProxy useDefaultCredentials="true" >
</defaultProxy>
</system.net>
</configuration>

Answer 1

The answer above didn't work for me, however DavidG's comment did solve my problem, so going to post as an answer in case it helps someone else.

For me, I was not running it as a sub-application, and a project that had been working for me no issue for over a year suddenly stopped working with this issue. Still not sure what changed. When I commented out or removed the <add name="aspNetCore".../> the error persisted, and then that line got automatically re-added.

To solve the problem, I added <remove name="aspNetCore" /> to the config file, right above the <add name="aspNetCore"... /> entry, and things started working again.