I have a client WinForms application consuming a .NET Web Service without an issues until a proxy is introduced. Once the communication goes through any proxy, IIS returns a 405: Method Not Allowed error on all method calls. I have stripped out anything that might be overtly causing issues and am running everything over a standard HTTP (i.e. NOT HTTPS) protocol. The proxy itself works just fine for standard browsing so there must be something on the server side that is blocking this call.