MSCRMEmail Event ID 23379

I get the following email in event viewer

#23379 - Could not verify the version of Dynamics 365 at http://XXXXXXXX. The server was unable to process the request due to an internal error.  For more information about the error, either turn on IncludeExceptionDetailInFaults (either from ServiceBehaviorAttribute or from the <serviceDebug> configuration behavior) on the server in order to send the exception information back to the client, or turn on tracing as per the Microsoft .NET Framework SDK documentation and inspect the server trace logs.

Any suggestions on how to diagnose it