HTTP Error 500.35 — ASP.NET Core does not support multiple apps in the same app pool

This happened to me recently when I was trying to resolve a different issue. The original issue was that my home page had randomly stopped working in my ASP.Net MVC application and I’m still unsure why this happened.

When I was looking at my original issue I looked at the launchSettings.json file in the projects properties. I changed the ApplicationUrl setting but this didn’t resolve my original issue so I reverted the value. This resulted in the error above. Frustratingly, restarting etc didn’t resolve this issue.

The solution that worked for me was to remove the .vs folder. I didn’t try it but I’ve since discovered that simply removing applicationhost.config from the .vs folder may be a preferable option. This makes some sense as the app pools are defined in there.