Trying to access one of these static files directly also fails and just shows the message “The page cannot be displayed because an internal server error has occurred.
In my case, the site was referencing the FontAwesome package which uses the WOFF file type. In the older IIS this MIME type was not registered so required a manual entry in the configuration. In the newer IIS this is handled natively and the manual configuration is now causing a problem rather than remediating one.
Check the web.config file for a reference to “woff” for example
<mimeMap fileExtension=”.woff” mimetype=”application/font-woff” />
and comment out or remove this line.
Refresh the page in your browser and it should now load correctly.