Plesk login page asks for authentication or redirect to IIS error message:
HTTP Error 401.2 - Unauthorized
You are not authorized to view this page due to invalid authentication headers.
Broken configuration of PleskControlPanel website in IIS.
Reconfigure Plesk website with Plesk Reconfigurator utlity: Open Plesk Reconfigurator > Repair Plesk installation > Plesk Services .