http://developers.de/blogs/damir_dobric/archive/2009/07/06/wcf-service-the-remote-server-returned-an-error-401-unauthorized.aspx  By connecting to WCF WebService with configuration shown bellow you may notice that the client could get sometimes in trouble. That is the exception can be thrown while invoking of some service operation: The remote server returned an error: (401enCommunityServer 2008 SP1 (Build: 30619.63)