This is an issue we see time to time that worries our customers. In most cases, this is a by-design benign warning that simply telling us a verification has been deferred to runtime.
If you select your Application pool in IIS Manager and choose the basic settings, you will see following window:
Now if you click on "Test Settings…", you may see a yellow icon next to Authorization section and a corresponding warning message as follows:
Here is the warning details: The server is configured to use pass-through authentication with a built-in account to access the specified physical path. However, IIS Manager cannot verify whether the built-in account has access. Make sure that the application pool identity has Read access to the physical path. If this server is joined to a domain, and the application pool identity is NetworkService or LocalSystem, verify that <domain><computer_name>$ has Read access to the physical path. Then test these settings again.
This is just a warning, not Error. Path authorization couldn't be tested at configuration time, but it will be tested at runtime.