Yuri Diogenes has blogged about how to troubleshoot an OWA publishing rule on ISA Server 2006.
Sometimes troubleshooting publishing rules can be really challenging. The main reason for that is because of the thin line between the published server and the edge firewall (in this case ISA Server). Where is it broken? Is my ISA Server not allowing the connection from outside or my published server that is not answering the request from ISA Server?
The sequence of articles written by Jim Harrison about RPC over HTTP helped to clarify how the protocols works and also to troubleshoot the main issues that happen when publishing Outlook Anywhere through ISA Server 2006.