If you are getting this message when installing Enterprise Portal in 2012 "Server was unable to process request. ---> Could not retrieve a valid Windows identity. ---> The message could not be dispatched because the service at the endpoint address 'net.pipe://localhost/s4u/022694f3-9fbd-422b-b4b2-312e25dae2a2' is unavailable for the protocol of the address." it's because of a stopped service in SharePoint.
Simply go to SharePoint Central Administration -> System Settings > Manage services on server and start the Claims to Windows Token Service.