Error: response message does not match the content type of the binding

Recently whilst creating a theme for an older wss site at a client, I ran onto this error working on a new development vm.

The content type text/html; charset=utf-8 of the response message does not match the content type of the binding (text/xml; charset=utf-8)

Make sure that Windows Communication Foundation HTTP Activation is enabled on the server and all will be good again.