Plesk interface is not accessible: Cannot read configuration file due to insufficient permissions

Symptoms

Plesk login page shows the following error in a web-browser:

CONFIG_TEXT: HTTP Error 500.19 - Internal Server Error
<...>
Error Code 0x80070005
Config Error Cannot read configuration file due to insufficient permissions
Config File \?\C:\Program Files (x86)\Plesk\admin\htdocs\web.config
<...>

Cause

The psaadm user does not have access to %plesk_dir%admin\htdocs\.

Resolution

1. Connect to the Plesk server via RDP.

2. Start Plesk Reconfigurator at Windows Start > All Programs > Plesk

3. Click Repair Plesk Installation > select Plesk File Security.

4. Click Check.