In my case, I was getting this error message because I was changed the service's namespace and services tag was pointed to the older namespace. I refreshed the namespace and the error disapear:
<services>
<service name="My.Namespace.ServiceName"> <!-- Updated name -->
<endpoint address=""
binding="wsHttpBinding"
bindingConfiguration="MyBindingConfiguratioName"
contract="My.Namespace.Interface" <!-- Updated contract -->
/>
</service>
</services>