WordPress is installed for a site with capital letters in name, e.g.
In WordPress admin dashboard > Settings > General the Site Address (URL) and WordPress Address (URL) contains capital letters as well:
Permalinks are enabled and set to a non-plain value;
In WordPress admin dashboard > Settings > Reading > Your homepage displays is set to A static page (select below) > Homepage as Sample Page;
The site shows the following error:
It is a Plesk bug with ID #PPPM-9702. It is considered to be fixed in the future Plesk updates.
Until a fix becomes available, one of the following workarounds can be used:
Change permalinks to Plain;
Change the site name to lowercase one, e.g.
Site Address (URL)and
WordPress Address (URL)to lowercase one, e.g.