Creating a WCF Service Library in Visual Studio 2008 on Vista x64 is troublesome when referencing an x86 DLL. A service that calls a 32-bit DLL is required to have a platform target of x86 to run on a 64-bit OS. When you do this, the WcfSvcHost throws a BadImageFormatException when you attempt to debug the service. There is a Creating a WCF Service Library in Visual Studio