 <p>Make sure you don't have a space character before or after the entry in the "Work with" field as you try to add the software site.</p> <p>Other than that, the software site is perfectly valid. Perhaps the server was just down at the time you tried it. You could also check to verify that there is no proxy or firewall filtering on your end. Try pinging the site or accessing it in some other way. If Eclipse can't talk to the site, it has no way of knowing that it is valid.</p>