By Anthony This write up assumes that you already have your Windows VPS/Server setup with Windows Server and Internet Information Server (IIS) installed, and your domain already working.
Once connected via rdp go ahead launch the Internet Information Services (IIS) Manager.
For this in IIS manager expand Server > Sites > Your Website > iso directory in left pane. From middle pane choose Directory Browsing and in the Right side Actions pane click Open Feature. At the moment you can see Directory browsing has been disabled by default. Click Enable. As you can see Directory browsing/listing is enabled.
Next go back to folder iso home. Click MIME Types and click Open Feature from Actions. Click Add button to Add new MIME Type. Use below information and click OK.
File name extensions: .iso
MIME Type: application/octet-stream
Next you will see new MIME type in the list.
That is it! Your site will now download the iso instead of erroring out.
Source: https://vcloud-lab.com/entries/microsoft-windows-server/part-2-configure-iis-server-to-allow-download–iso-files