SharePoint 2010 RSS feed and TMG: “Proxy Authentication required” error

Problem: When you configure a webpart for RSS feeds in a SharePoint 2010 site, you receive the following error: ProtocolError occured trying to complete the request. The server returned a status code of : ProxyAuthenticationRequired and the status description is : "Proxy Authentication Required ( Forefront TMG requires authorization to fulfill the request. Access to […]