502 proxy error. The request is not supported(50) while accessing websites from the web proxy clients
This is on ISA /TMG product blog(https://blogs.technet.com/b/isablog/archive/2010/05/24/error-502-proxy-error-the-request-is-not-supported-50-while-trying-to-access-websites-from-web-proxy-clients-behind-isa-server-2006.aspx)