Yum failing with "This system is not registered with CLN" message

Symptoms

When trying to perform software installation or server updates you may receive an error from Yum with the following:

root@server [~] # yum makecache
Loaded plugins: fastestmirror, rhnplugin, universal-hooks
Profilename: fdce.com.br
Error communicating with server. The message was:
Yours `rhn-client-tools` is outdated, please update it using `yum update rhn-client-tools -y`.
This system is not registered with CLN.
You can use rhn_register to register.
CLN support will be disabled.

Description 

This error indicates you either do not have a CloudLinux license, or the license has expired, preventing your system from receiving updates from their network.  You can check if the license was purchased through cPanel here:

https://verify.cpanel.net/app/verify

or through CloudLinux here:

https://cln.cloudlinux.com/console/check-license

Workaround

If your system is not licensed you'll need to either purchase a license, which can be done through the cPanel Store, or you'll need to uninstall the CloudLinux software.