Good day.
Your WS web server sends SOAP responses using "Transfer-Encoding : chunked" type. However, .NET WCF infrastructure (based on WebHttpClient, ...) does not correctly implement HTTP 1.1 protocol and cannot handle this type of transfer encoding, so this creates problem when one tries to access your Hypertext validation SOAP web-service using .NET WCF infrastructure.
Is it possible to reconfigure your web-server and disable "chunked" encoding for SOAP responses somehow ?