Need help with ISA proxy


I can’t seem to get it to work with a proxy. I tried every combination.
I receive a cycle of alerts not allowing me to close the application properly.

Proxy error: Can’t connect to proxy server.

followed by this message:

HTTP/1.1 500 (the SSL port specified is not allowed) The ISA server is not configured to allow SSL requests on this port.

Can anyone help me with the configuration of the proxy settings?
Here they use a Firewall client for Microsoft ISA server.