I have a VS2010 (RTM) solution which contains:
WCF Service project
Console WCF client project
Class project for DataContracts and members
Class project for some simple classes
I successfully added a service reference in the console client project and ran the client. I then did a long dev cycle repeatedly modifying the service then updating console service reference. I then changed the namespace and assembly names for the projects as well as the .cs using references and app.config. I of course missed some things as it would not build so I eventually removed the project references and the service reference, cleaned and built successfully.
I then attempted to add the service reference again, it discovered it but threw the “Object reference not set to an instance of an object” when OK'ing. Fix in answer below...