To state the obvious, this error means that compiled service does not match the source code i.e. source code has changed since service run. Make sure you rebuild your solution.
What I do to debug WCF services is to have 2 instances of Visual Studio. One runs a WCF service hosting app (console) and the other runs a client. Make sure you are running debug version. It should work (and debug) fine as long as the client can successfully connect to your service.
You get "The breakpoint will not currently be hit."
The breakpoint will not currently be hit.
when a module with that breakpoint has not been loaded (yet). Your service will not be loaded until a client connects.