This exception appears when you try to synchronize the time with a remote server through the System Time module of Webmin:
And the operative system doesn't have the NTP package available from the CLI. Depending on your operative system, you can easily install with the following command for Debian/Ubuntu:
sudo apt-get install ntp
If you are in CentOS or Redhat based systems, you can install this package with yum:
sudo yum install ntp
After the installation of this package, you may now synchronize using a time server without any problem.
Happy coding ❤️!