I ran into an issue with one of my WCF services and was having the quite a time trying to track it down, especially since it was failing before it was getting to the actual service. I came across a nice way of tracing the call all the way through the process. Add the following section to your web.config file:
initializeData= "C:\Logs\Traces.svclog" />
This will create a trace file that you can open up in the Microsoft Service Trace Viewer. You can read about the details here.
Quick note – Don’t forget to remove it when you’re done!