I stumbled on this error when browsing a new ASP.NET site I was configuring. This error was caused on my server because the Application Pool identity that was running the ASP.NET website process had not given permissions to guest users. To resolve this
- In IIS Manager select the website
- Go into the Authentication settings in the content page on the right
- Go into the properties for the guest user (Anonymous Authentication)
- Change the anonymous user identity to “Application pool identity”
Why is this not the default?