Also check for a firewall running on your OpenACS machine. Use the following 2 commands to remove any firewall rules.
iptables -F
ipchains -F
Also, if you haven't already make sure you turn off "Show Friendly HTTP Error Messages" in your Internet Explorer configuration.
(That setting would be more accurately called "Hide Relevant Info and Cause Mass Confusion" but I doubt they'll change the name for me)
