1. In the following file

C:\Windows\System32\inetsrv\config\applicationHost.config

Ensure the following

<section name="requestFiltering" overrideModeDefault="Allow" />

2

This is the web.config file

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
         <handlers>
           <clear />
            <add 
                name="StaticFile" 
                path="*" verb="*" 
                modules="StaticFileModule,DefaultDocumentModule,DirectoryListingModule" 
                resourceType="Either" 
                requireAccess="Read" />
        </handlers>
        <staticContent>
            <mimeMap fileExtension=".*" mimeType="application/octet-stream" />
        </staticContent>
        <security>
            <requestFiltering>
                <fileExtensions allowUnlisted="true">
                    <remove fileExtension=".config" />
                    <add fileExtension=".config" allowed="true" />
                </fileExtensions>
            </requestFiltering>
        </security>
    </system.webServer>
</configuration>