The Federation Service encountered an error while loading the trust policy. A custom claim collection in the trust policy ...

The Federation Service encountered an error while loading the trust policy. A custom claim collection in the trust policy contains a duplicate item. 
Collection type: CustomClaimCollection 
Custom claim name: %1 
Custom claim value: %2 

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 duplicate item from the collection.