There is no domain-level user login to Parallels Plesk Panel after upgrade from 9.x to a newer version 11.x. It is not possible to create control panel user with permissions to manage only one domain?
According to Upgrade from Earlier Panel Versions in Plesk 11.5:
In Panel 11, there are no client accounts and domain administrator accounts. For users who need to resell hosting services and host their own websites, you will set up reseller accounts. For users who do not need to resell hosting services, but only host their own websites, you will set up customer accounts.
According to What Happens When You Upgrade or Migrate to Panel 10
Domain administrator accounts are converted to user accounts, which are assigned to the customers who own the corresponding domains.
Parallels Plesk Panel 10/11 allows creating additional auxiliary users with domain administrator permissions. For that login to Parallels Plesk Panel as admin and follow:
Subscriptions > %subscription% > Manage hosting (or Open in Control Panel) > Users
User Role > Create User Roleto create new User Role with required permissions.
User Accounts > Create User Accountto create new Auxiliary User Accounts, assign it to the role you created previously.