This is an error visible in the web browser when connecting to a HTTPS web site behind an ISA Server.
The problem is that the firewall access rule for this web site in ISA Server is forwarding the requests to an internal server on a port that it is not listening on. For example you connect to https://server.example.com and the ISA Server forwards this request to http://internalsrv. On the Bridging tab check that the mentioned port(s) are actually working on the internal server. For example if you are listening in ISA Server on 443 for a SSL connection and the SSL/HTTPS port is ticked make sure that the port is 443, and that the web server internally is listening on 443. If its another number make sure that it is meant to be the other number and not really 443 or not ticked at all. Ditto for the HTTP port, which is 80 by default.