- Plesk 12.0 for Linux
- Subscription gets locked when setting any SSL in Subscriptions > example.com > Websites&Domains > Hosting Settings > Security > Certificate
- In subscription's service plan Hosting settings management is not granted (Home > Service Plans > Service_plan > Permissions)
This is expected behavior: since Hosting settings management is not granted for the corresponding subscription any changes in Hosting settings, including setting SSL certificate will get subscription locked.
Grant the Hosting settings management in Service Plans > Service_plan > Permissions
Additional information about Service Plans can be found in Plesk documentation.