Normally the answer to this is to reinstall the browser.
This error indicated that your web browser is unable to do a DNS lookup on the website you are trying to connect to.
If you are able to connect to the internet with another browser, reinstall chrome.
If you are not able to connect, check your IP settings in Ubuntu and make sure you have DNS servers assigned (IFCONFIG will do it)
If your DNS settings are ok, its going to be a problem with yoru internet connection. I've also seen one case a long time (a couple of months) ago where reinstalling NIC (WiFi or Ethernet) drivers sorted this problem out on a different browser... always worth a shot.