Grrr... Just wasted lots of time on a stupid mistake due to misleading error message. I hate it when that happens. I usually do self-hosting for my WCF services, but on a project I am working on we wanted to host in IIS. I was focused on the security aspects - trying to get Integrated Windows security on a web site, using impersonation to call the service under the client's credentials, protecting the service with Integrated Windows Authentication and turning off anonymous access in IIS. I was trying...