[Resolution] Verify that the built-in Users group has Read, List, and Read & Execute permissions for each Team Foundation Web site directory and virtual directory on which Team Foundation relies. For more information, see How to: Change the Access Control List Permissions for a Directory. Also, verify that the service account for Team Foundation has full access to the MachineKeys directory. For more information, see How to: Change the Security Permissions for the MachineKeys Directory. [Problem] 
Directory or folder permissions are not set correctly.