If your site is not loading and in the logs you see:

GET / |41|ASP_0131|Disallowed_Parent_Path HTTP/1.0

You will need to enable "Parent Paths" for your site directory. To do this log in to your Plesk control panel and under the domain affected click on "Virtual Directories". Now from the top options click on "Directory Properties" and on the next page make sure the option "Allow to use parent paths" is selected. Save and this error should now be resolved.