If I start up Microsoft Visual Studio, create a standard \"WCF Service Library\", and compile it, it works perfectly.
However, if I go into Properties..Build and set
Your problem is actually the WCF Test Client complaining that your WCF Service Library is 32bit. This is because by default, the WCF Test Client always runs in 64 bit mode.
Rather than going to the lengths of changing to a WCF Service Application so you can debug, I found the following steps on this blog which makes the WCF Test Client run in 32bit mode - and therefore you will not see the error you have posted.
"cd" to the directory where your copy of WcfSvcHost is located.
Execute the command "corflags /32BIT+ /FORCE WcfSvcHost.exe"
Execute the command "corflags /32BIT+ /FORCE WcfTestClient"
Copy the files back to where you found it.
Now your WcfSvcHost and WcfTestClient will be running in 32 bit mode, and you can debug away!
I found two good methods to solve this: