When we create a link to an external web site such as www.cnn.com using the RadEditor (6.3.0.0) on our SP2010 farm we are getting an error that says this:
"cannot find this location in the current site location"
"the URL may refer to an external web site for to a location in the site collection that does not exist or you do not have the right to access"

When I bring up a browser on the SharePoint server themselves I can access those sites.