What is the web page you are trying to open: http://gwt.google.com
?
Does this page load if you write the url directly in the address box of your browser ?
Does Internet work in that computer? try to access google or any other page.
This error is a clear case of a miss-configuration on your PC internet stack:
The server at gwt.google.com can't be found, because the DNS lookup failed.
What does return this command in your console?
nslookup gwt.google.com
EDITED:
After reading your comments I figure out what is happening: your browser has not the gwt-plugin installed, so the first time it connects to a gwt-dev-mode app, the app redirects it to the gwt site to download the plugin and install it.
You have either, connect this computer to the internet to install the plugin the first time it is requested, or download the plugin and install it manually.