The Federation Service encountered an error while loading the trust policy. An account partner is misconfigured. The AllowedTrustedWindowsDomains ...

The Federation Service encountered an error while loading the trust policy. An account partner is misconfigured. 

The AllowedTrustedWindowsDomains field is configured for an account partner for which Windows trust is not enabled. 
Field: AllowedTrustedWindowsDomains 

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. Either enable Windows trust on the account partner or remove the AllowedTrustedWindowsDomains field.