The service class of type {0} both defines a ServiceContract and inherits a ServiceContract from type {1}. Contract inheritance ...

The service class of type {0} both defines a ServiceContract and inherits a ServiceContract from type {1}. Contract inheritance can only be used among interface types.  If a class is marked with ServiceContractAttribute, it must be the only type in the hierarchy with ServiceContractAttribute.  Consider moving the ServiceContractAttribute on type {1} to a separate interface that type {1} implements.