when you hit "Build Library" under HII Driver Management you should see the Root web URL from wich the drivers.db3 is downloaded.
Can you try to call the URL in your browser?
Maybe it is a simple error caused by your IIS not managing .db3 extension. If so you can add a mime type for .db3 or modify the web.config
Tried your suggestion. Can easily pull all the info in the browser.
Maybe anonymous access is the cause of the problem ? Try to configure "Connect As" option to avoid anonymous access problem on the virtual directory.
Amagi's answer is a good advice, i personally add mime type .* application/octet-stream on all my preferred servers.