active directory federation server secondary node is giving HTTP Error 503

active directory federation server secondary node is giving HTTP Error 503. The service is unavailable.

when i try to access the link using the sever name 

https://myserver.mydomain/FederationMetadata/2007-06/FederationMetadata.xml

i am seeing this in the event log of the adfs

There was an error in enabling endpoints of Federation Service. Fix configuration errors using PowerShell cmdlets and restart the Federation Service.

Additional Data
Exception details:
System.ArgumentNullException: Value cannot be null.
Parameter name: certificate
   at System.IdentityModel.Tokens.X509SecurityToken..ctor(X509Certificate2 certificate, String id, Boolean clone, Boolean disposable)
   at System.IdentityModel.Tokens.X509SecurityToken..ctor(X509Certificate2 certificate)
   at Microsoft.IdentityServer.Service.Configuration.MSISSecurityTokenServiceConfiguration.Create(Boolean forSaml)
   at Microsoft.IdentityServer.Service.Policy.PolicyServer.Service.ProxyPolicyServiceHost.ConfigureWIF()
   at Microsoft.IdentityServer.Service.SecurityTokenService.MSISConfigurableServiceHost.Configure()
   at Microsoft.IdentityServer.Service.Policy.PolicyServer.Service.ProxyPolicyServiceHost.Create()
   at Microsoft.IdentityServer.Service.SecurityTokenService.STSService.StartProxyPolicyStoreService(ServiceHostManager serviceHostManager)