Hello,
The error message you have received is default Plesk error page. I would suggest you to disable Custom Error Documents option through Plesk which will help in getting to know the actual error message. You can disable ‘Custom Error Documents’ through the following steps.
Login to Plesk control panel >> Select ‘Domains’ option >> Select domain name >> Select ‘Setup’ option >> Remove tick from ‘Custom Error Documents’ option >> OK
If problem still persists, you can open ticket at our support email address with exact link for further investigation. Our technical support will assist you further in this regard.
