The Federation Service encountered an error while loading the trust policy. The Active Directory Domain Services account ...

The Federation Service encountered an error while loading the trust policy. The Active Directory Domain Services account store has been configured to fetch user principal name (UPN) from a custom Lightweight Directory Access Protocol (LDAP) attribute. 

If this error occurs during startup of the Federation Service, the Federation Service will be not be able to start, and all requests to the Federation Service will fail until the configuration is corrected. If this error occurs while the Federation Service is running, the Federation Service will continue to use the last trust policy that was loaded successfully. 

User Action 
This error should occur only if the trust policy file has been modified without use of the AD FS administrative tools. Remove the custom LDAP attribute for UPN from the Active Directory Domain Services account store configuration.