I have recently upgraded SharePoint 2013 farm from RTM to SP1. I am repeatedly getting errors  No windows identity for Domain Name\User in ULS log. Some users who was earlier able to access to site is not able to access site.

Few questions to quickly check with you..

1. Have you re-run your SharePoint Configuration Wizard after you upgraded from RTM to SP1? Its very important to re-run SharePoint Configuration Wizard to ensure SharePoint Config DB is updated with latest changes in the farm.

2. If you have performed the above step but still face issues, have you restarted your SharePoint Server after re-running your SharePoint Configuration Wizard? If not please restart the server.

3. If not anyone of the above, then have you changed your authentication type for your web application in Central Admin. Example, from Classic Authentication to Claim Based Authentication?

Thanks for your reply.

1 SharePoint Configuration Wizard re-run - Done

2 Restart Server - Done

3 Authentication Type changed - No

Still I am facing issue. I am seeing issue related to feedcahce also. 

Now go to Central Administration > System Settings > Manage Services on Server and check if Claims to Windows Token Service is in 'Started' mode. If you find this service in 'Stopped' mode then please Start it. And now check your ULS logs for the error and also check if users can access the site now.