The Federation Service encountered an error while loading the trust policy. The trust policy file path is not valid. Path: ...

The Federation Service encountered an error while loading the trust policy. The trust policy file path is not valid. 
Path: %1 

The Federation Service will be not be able to start, and all requests to the Federation Service will fail until the configuration is corrected. 

User Action 
Correct the configuration to specify a fully qualified file path to an existing trust policy file. This configuration can be corrected in the web.config file or by using the AD FS administration console.