Check if the ControlCenter service is up and running. To do so, open an SSH connection to the appliance and run the command:
service vco-configurator status
the status should be RUNNING. If needed, you can start / restart the service with the following commands, respectively:
service vco-configurator start
service vco-configurator restart
You can also try to reset the authentication with the following command:
/usr/lib/vco/tools/configuration-cli/bin/vro-configure.sh reset-authentication
Let's check if you'll be able to open ControlCenter UI at this point. If not, then you can try to manually change the authentication provider configuration, stored in the file /etc/vco/app-server/vmo.properties, by changing the line
ch.dunes.authentication.provider = vsphere
to
ch.dunes.authentication.provider = ldap
saving the file, and then restarting ControlCenter service.