It's impossible to access website - authorization prompt appears.
There may be several reasons of this issue. To determine them, the following conditions need to be checked:
1\. There should be read + execute permissions for IUSR\ <ftp\ user> on the domain index page.
2\. Root directory for the domains can be under Parallels Plesk Panel protection.
3\. Passwords for system user and IIS user can be out of synchronization.
- Go to %plesk\_vhosts%\\domain.com\\httpdocs directory and check permissions for IUSR\ <ftp\ user> account.
2\. It can be checked using Plesk Control Panel. Go to Plesk, domains, domain.com, Protected URLs .
3\. The password for IIS user can be synchronized using the following command:
"%plesk_bin%\\websrvmng.exe" --update-anon-password --domain-name=domain.tld
Note: this feature is available starting with Parallels Plesk Panel 7.5.4 and the latest hotfixes.