This is by design. IIS will show the default document listed in that folder. If no default documents exist, then it will show that error. By default, directory browsing is disabled. Enabling directory browsing presents a risk to your DNN site because anyone who knows the URL of a file can bypass DNN's built in security and download it directly.
If you still want to enable directory browsing, please follow these instructions:
- Log into your Plesk Control Panel.
- From the Home tab, go to [Manage Hosting] > Websites & Domains tab > Show More > Virtual Directories >Directory Properties.
- Check the Directory browsing box.
- Click OK.