Claims to Windows Token Service (c2WTS) may not start automatically when you reboot your server (don’t blame SharePoint for that)
I know a large number of people who believe that Claims to Windows Token Service is a SharePoint feature. They are mistaken, c2WTS is part of Windows Identity Foundation (WIF) which is one of the pre-requisites for SharePoint. SharePoint indeed relies on c2WTS for delegation. It works this way: c2WTS extracts UPN claims from non-Windows