In order to set ASP.NET permissions you will need to use the Plesk IIS WP User.
- Login to your Plesk Control Panel
- Click on domains and then the domain name that you wish to set permissions for.
- Click on file manager.
- Browse to the file or folder you wish to set permissions on.
- Click on the lock icon on the far right.
- Click on the Plesk IIS WP User account.
- On the right set the permissions that you need
- Click OK.